The substantial relationship test under Rule 1.9 asks a single question: could the lawyer have learned confidential information in the earlier representation that would be relevant to the new matter? If the answer is yes, and the new client’s interests are materially adverse to the former client’s, the lawyer is disqualified unless the former client gives informed consent in writing.1American Bar Association. Model Rules of Professional Conduct – Rule 1.9: Duties to Former Clients The rule exists to protect something basic about the attorney-client relationship: you should be able to speak candidly with your lawyer without worrying that your secrets will later be used against you.
The Three Elements Courts Look For
Rule 1.9(a) blocks a representation when three things line up. A former attorney-client relationship existed. The new matter is the same as, or substantially related to, the old one. And the new client’s interests are materially adverse to the former client’s.1American Bar Association. Model Rules of Professional Conduct – Rule 1.9: Duties to Former Clients
Most fights happen on the second element. Courts compare the two matters along several axes: the evidence involved, the legal theories at stake, and the specific issues in dispute. A lawyer who drafted a company’s licensing agreements cannot later represent someone attacking those agreements. The factual overlap is too tight to pretend the lawyer walked away from the first engagement empty-handed on negotiating positions, business vulnerabilities, or litigation posture.
The test is not whether the former client can prove the lawyer actually received specific secrets. It is whether, given the scope of the prior engagement, the lawyer would ordinarily have been exposed to information useful in the new case.2Justia Law. Analytica, Inc. v. NPD Research, Inc., 708 F.2d 1263 (7th Cir. 1983) That shift matters: the former client never has to disclose what was shared in order to prove the conflict.
General Knowledge Versus Specific Confidences
A recurring question is whether broad familiarity with a former client’s business triggers the rule. Most courts have rejected the “playbook” theory, which treats general knowledge of a company’s litigation philosophy or management style as enough to disqualify a lawyer from any future case against that client. California courts, for instance, have held that general knowledge of an employer’s anti-discrimination policies does not automatically substantially relate to a later discrimination suit. What matters is a concrete link between specific confidential information the lawyer obtained and the actual issues in the new case.
The line is not perfectly bright. Some courts have disqualified lawyers who absorbed strategically valuable knowledge, like a former client’s patent prosecution approach or trade secret protection strategy, even when the specific transactions in the two matters differed. Surface-level familiarity with how a company operates rarely triggers the rule. Deep exposure to a client’s thinking on a particular subject can.
What Material Adversity Means
A substantial relationship alone is not enough. The new representation must also be materially adverse to the former client. ABA Formal Opinion 497 reads this as the lawyer either litigating or negotiating against the former client, or attacking the work done for the former client on behalf of a current client, in the same or substantially related matter.3American Bar Association. ABA Issues New Guidance on Definition of Material Adverseness in Client Representation
Take a lawyer who defended a corporation in a product liability case. If that lawyer later represents a plaintiff suing the same corporation over a defect in the same product line, the adversity is plain. The lawyer would have to attack the safety protocols and manufacturing processes they once defended.
Adversity does not require open litigation. A lawyer who helped a former client negotiate a favorable lease term, and who then advises a new client on how to challenge that term, is materially adverse even without a lawsuit. The question is whether the new engagement puts the lawyer in a position to concretely undermine the former client’s interests.
The Presumption That the Lawyer Received Confidences
Once a court finds a substantial relationship, most jurisdictions presume the lawyer received confidential information during the earlier representation. At the individual-lawyer level, this presumption is effectively conclusive. The former client is not required to describe what specific secrets they shared, and the lawyer cannot escape the bar by claiming they forgot the details or never looked at certain files.1American Bar Association. Model Rules of Professional Conduct – Rule 1.9: Duties to Former Clients
Forcing the former client to identify the exact information at risk would gut the protection. Picture a former client having to describe their trade secrets or litigation strategy in open court just to prove a conflict exists. The rule avoids that trap by tying disqualification to the relationship between the matters rather than to a forensic accounting of what the lawyer actually learned.
A second presumption operates at the firm level. When an individual lawyer is presumed to have confidential information, courts presume that information was shared with colleagues. The firm-level presumption can be rebutted, but the bar is high. Informal assurances or after-the-fact affidavits are generally not enough; the firm must show, with clear proof, that effective screens kept the information away from the lawyers working the new matter.
When a Lawyer Changes Firms: Rule 1.9(b)
One of the most practically important parts of Rule 1.9 covers lateral moves. Under Rule 1.9(b), a lawyer whose former firm represented a client cannot represent someone adverse to that client in the same or a substantially related matter if two things are true: the new client’s interests are materially adverse to the former client’s, and the lawyer personally acquired protected information material to the matter.1American Bar Association. Model Rules of Professional Conduct – Rule 1.9: Duties to Former Clients
The distinction from 1.9(a) matters. A lawyer who personally represented the former client faces a broad bar because the lawyer is presumed to have confidences. A lawyer who was merely at the firm that handled the matter is only conflicted if they actually gained material confidential information during that time. A junior associate in a 500-lawyer firm who never touched the case and had no access to the relevant files is not disqualified just because a partner across the country handled it.
This is the rule that governs lateral hiring in big firms. Every move triggers a check: at the departing firm, at the receiving firm, and against the receiving firm’s existing engagements. Missing a conflict can force a firm off a lucrative matter after the problem surfaces in litigation.
The Standalone Duty Under Rule 1.9(c)
Even where the substantial relationship test is not triggered, Rule 1.9(c) imposes a duty that outlasts the representation. A lawyer who previously represented a client may not use information from that representation to the former client’s disadvantage, and may not reveal that information, unless it has become generally known or the Rules otherwise permit disclosure.1American Bar Association. Model Rules of Professional Conduct – Rule 1.9: Duties to Former Clients
This provision catches situations the substantial relationship analysis misses. Two matters might not be “substantially related” in any traditional sense, but if a lawyer learned something specific in the first engagement and uses it against the former client in an unrelated context, 1.9(c) still prohibits that conduct. The duty extends to lawyers whose former firm handled the representation, not just lawyers who personally handled it.
Waiver Through Informed Written Consent
A conflict under Rule 1.9 is not absolute. The former client can waive it, but only through informed consent, confirmed in writing.1American Bar Association. Model Rules of Professional Conduct – Rule 1.9: Duties to Former Clients “Informed” is doing real work in that phrase. The lawyer must explain the facts creating the conflict, describe the risks, discuss how prior knowledge could be used disadvantageously, and outline the alternatives.4American Bar Association. Model Rules of Professional Conduct – Rule 1.0 Terminology – Comment
A signature on a boilerplate form is not enough. The former client needs to understand how the prior work could overlap with the new case, what information is at risk, and what the consequences could be. Whether the former client has independent counsel reviewing the waiver matters. A sophisticated corporate client with in-house legal advisors needs less hand-holding than an individual whose last engagement with the lawyer was a personal matter years ago. Silence is not consent; the lawyer needs an affirmative response.
Imputation to the Rest of the Firm
When one lawyer in a firm is disqualified under Rule 1.9, the conflict generally spreads to every other lawyer there. Rule 1.10(a) treats lawyers in the same firm as a unit for conflict purposes, reflecting the reality that they share information and have a shared financial interest in each other’s work.5American Bar Association. Model Rules of Professional Conduct – Rule 1.10: Imputation of Conflicts of Interest: General Rule Handing the file to a different partner down the hall does not fix the problem.
The 2009 Screening Exception for Lateral Lawyers
In 2009, the ABA amended Rule 1.10(a)(2) to add an exception. When a lawyer’s conflict arises from work at a prior firm, the new firm can avoid imputed disqualification by setting up a timely ethical screen. The screened lawyer must be walled off from the matter and receive no share of the fee. The firm must promptly notify the affected former client in writing, describe the screening measures, and certify compliance at reasonable intervals if asked.
The screen has to be real. Courts look for restricted access to the physical and electronic file, a strict no-discussion rule, exclusion from fee participation, and implementation the moment the conflict is identified. A wall set up weeks after the lawyer joined the firm, or one that exists only on paper, will not hold up. The exception also does not reach a lawyer who personally represented the former client at the current firm; in that situation, firm-wide disqualification is the default unless the former client consents.
What Happens When Rule 1.9 Is Violated
Three categories of consequences can follow, and they can stack.
- Disqualification. A court can remove the lawyer, and often the entire firm, from the case. This is the most immediate consequence and the one litigants typically seek through a motion.
- Professional discipline. State bar authorities can impose sanctions ranging from a reprimand to suspension or disbarment. In one case, an attorney was suspended for 150 days after drafting financial documents for a client and later representing the lender in a collection action against that client’s estate.6State of Illinois Office of the Illinois Courts. When the Past and Present Diverge: A Brief Discussion of Former Client Conflicts of Interest Under Rule 1.9(a)
- Civil malpractice liability. Former clients can sue for compensatory damages covering financial losses from the breach of loyalty. Courts have also ordered disgorgement of legal fees, requiring the lawyer to return what the former client paid. For disgorgement, the former client only needs to show the lawyer breached the duty of loyalty, not that the breach caused a specific dollar amount of harm.
Filing a Motion to Disqualify
When a former client believes opposing counsel has a conflict, the usual remedy is a motion to disqualify filed in the court hearing the case. Two procedural issues trip up many movants.
Standing
Most jurisdictions limit standing to the current or former client of the conflicted attorney. A party who has never had an attorney-client relationship with the lawyer generally cannot seek disqualification, even if the conflict looks obvious. The moving party has to show a tangible interest in the opposing side’s choice of counsel, not a general objection.
Timeliness
Waiting too long can backfire. Courts apply a form of laches, weighing how far into the litigation the motion comes and how long the movant knew about the potential conflict before acting. A delay of two and a half years after learning of a conflict has been treated as implied consent, while an eight-month delay was found acceptable. The dividing line often turns on whether the timing reflects a genuine fairness concern or a tactical move to disrupt opposing counsel late in the case. A court that reads the motion as strategic may deny it even when a real conflict exists.
Related Rules That Are Not Rule 1.9
Two situations look like Rule 1.9 but are governed by different rules, and the test is different in each.
Former government lawyers are covered by Rule 1.11, not the standard substantial relationship test. Rule 1.11 asks whether the lawyer participated “personally and substantially” in the matter while in government service; if so, the lawyer cannot represent a private client in that matter unless the agency gives informed written consent.7American Bar Association. Model Rules of Professional Conduct – Rule 1.11: Special Conflicts of Interest for Former and Current Government Officers and Employees Rule 1.11 also allows the firm to avoid imputed disqualification through timely screening and notice to the agency, a more permissive approach than Rule 1.10.
People who consult a lawyer but never hire one are covered by Rule 1.18. A lawyer who received information from a prospective client that could be significantly harmful to that person cannot represent an adverse party in the same or a substantially related matter.8American Bar Association. Model Rules of Professional Conduct – Rule 1.18: Duties to Prospective Client An initial consultation is not risk-free for the lawyer: if someone describes their divorce in detail and then hires someone else, the lawyer may be blocked from representing the spouse.