A person who is mentally incompetent can get married if, at the moment of the ceremony, they understand what marriage is and the basic obligations it creates. The legal threshold is lower than most people expect, and a diagnosis of dementia, intellectual disability, or mental illness does not by itself prevent a valid marriage. If the person truly lacked that understanding at the time of the wedding, the marriage is not automatically wiped out. It is voidable, meaning it counts as a legal marriage with full legal effects until a court annuls it.
What Capacity to Marry Actually Requires
The test comes down to two things: whether the person understands the nature of the marriage relationship, and whether they understand the basic responsibilities it creates, such as committing to another person and mutual support. They do not have to grasp every legal or financial consequence, like tax treatment or inheritance rules.
The capacity required to marry is lower than the capacity required for many other legal acts. A person may have enough understanding to marry even if they lack the capacity to make a will, sign a complex contract, or grant a power of attorney. Committing to a spouse is a simpler idea than directing how a multi-asset estate should be distributed.
The Uniform Marriage and Divorce Act, adopted in some form by many states, lists lack of mental capacity as a ground for invalidating a marriage where “a party lacked capacity to consent to the marriage at the time the marriage was solemnized, either because of mental incapacity or infirmity or because of the influence of alcohol, drugs, or other incapacitating substances.” The focus is the person’s state of mind at the specific moment the marriage was entered, not their general diagnosis.
Lucid Intervals
Someone who has been found legally incompetent, or who has a cognitive condition, may still have periods of clarity where they fully understand what they are doing. The law calls these lucid intervals. A marriage entered during one of them can be perfectly valid, even if the person lacks capacity at other times.
That is why the fight in a contested case usually turns on the wedding day itself. Witness accounts of how the person behaved and what they seemed to understand, medical records close in time to the ceremony, and psychiatric opinion all matter. A doctor’s general statement that the person has dementia is not enough on its own. The question is whether the impairment prevented understanding on that specific day.
Marriage When Someone Has a Guardian
Guardianship does not automatically strip away the right to marry. Because marriage is a fundamental constitutional right, courts are reluctant to remove it entirely, and many guardianship orders are tailored to the ward’s specific limitations. If the order does not explicitly restrict the right to marry, the ward may still hold it.
In practice, oversight is usually involved. Some states require the guardian’s consent before the ward can marry. Others require the ward, the guardian, or the intended spouse to petition the court that oversees the guardianship, which then holds a hearing to evaluate whether the ward has the required understanding and whether the marriage serves their interests rather than exposing them to exploitation. The standard the court applies is the same as for anyone else. The burden of proof typically falls on whoever is opposing the marriage, because denying the right to marry is a serious restriction of liberty.
Voidable, Not Void
This distinction matters more than families expect. A void marriage, like one involving bigamy or close blood relatives, is treated as though it never existed and needs no court action to undo. A marriage entered by someone who lacked capacity is voidable. It is a real marriage with full legal effect until a court formally annuls it.
All the usual consequences kick in: property rights, inheritance rights, changes in benefit eligibility, and spousal obligations. Those remain in place unless and until someone obtains an annulment. Families who suspect a loved one was married while lacking capacity sometimes assume the marriage does not count. It does count, and undoing it requires affirmative legal action.
Ratification If Capacity Returns
If the person regains capacity after the marriage and continues living with their spouse as a married couple, the marriage can become permanently valid through ratification. By accepting the benefits of married life while fully able to understand the relationship, the person has effectively confirmed their consent. No formal declaration is needed. It happens through conduct: continuing to cohabit, sharing finances, and behaving as married partners after regaining the capacity that was missing at the ceremony. Once that occurs, the window to annul closes.
Who Can Challenge It
Because the marriage is voidable, only certain people have standing. The incapacitated person has the clearest right, and if they cannot act on their own, their guardian can file for them. In many states, relatives with a direct interest may also bring a challenge. The other spouse may have standing too, though courts are more skeptical of a challenge brought by a spouse who knew about the incapacity before the wedding.
Getting the Marriage Annulled
The process starts with a petition for annulment, usually filed in the family court with jurisdiction over the marriage. The petition identifies the parties, states the date and place of the marriage, and alleges that one party lacked capacity at the time of the ceremony. When a guardian is filing on behalf of the incapacitated person, the petition normally includes documentation of the guardianship.
The other spouse must be formally served and given a chance to respond. If they contest the annulment, the case goes to a hearing. The petitioner carries the burden of proving the person lacked capacity. Medical records are the backbone of most cases, supplemented by expert psychiatric testimony and accounts from people who observed the person around the time of the wedding. If the judge is convinced, the court issues a decree of annulment declaring the marriage invalid.
Timing and the Death Problem
Most states do not impose a strict filing deadline for annulments based on mental incapacity while the person remains incapacitated. A challenge can typically be brought during the incapacity, by the person after regaining capacity, or by relatives during the person’s lifetime. The main risk of delay is ratification. Rules vary by state, so local law on timing matters.
Waiting until after death is far worse. Some states allow annulment proceedings to continue or begin after one spouse has died, but the practical effect is often limited. Property and inheritance rights generally depend on whether the couple was legally married at the moment of death, and many state laws require the annulment to have been in effect before the death to strip the surviving spouse of those rights. A predatory marriage that was never challenged during the person’s lifetime may be nearly impossible to fully unwind afterward. That is the strongest argument for acting quickly.
Financial and Legal Fallout to Weigh
A marriage involving a person with a cognitive disability can quietly rearrange their income, benefits, and estate plan. These consequences are worth understanding before deciding whether to challenge a marriage, or whether to allow one to proceed.
SSI
Marriage carries a significant penalty for anyone receiving Supplemental Security Income. In 2026, the federal SSI payment for a single individual is $994 per month. When two SSI recipients marry, their combined payment as a couple drops to $1,491 per month, 25% less than what they would receive living separately.1Social Security Administration. SSI Federal Payment Amounts for 2026
Asset limits follow the same pattern. A single SSI recipient can hold up to $2,000 in countable resources. A married couple’s limit is $3,000, not $4,000.2Social Security Administration. Who Can Get SSI
When an SSI recipient marries someone who does not receive SSI, the situation can be worse. The Social Security Administration applies deeming rules, which treat a portion of the non-SSI spouse’s income and resources as available to the SSI recipient. That can reduce or completely eliminate SSI eligibility depending on how much the spouse earns.3Social Security Administration. 20 CFR 416.1163 – How We Deem Income to You From Your Ineligible Spouse For a person with a cognitive disability who depends on SSI for basic living expenses, a marriage they did not fully understand could cut off the income that pays for their housing and care.
Medicaid
Marriage can also affect Medicaid eligibility. A spouse’s income and resources may be counted in determining whether the recipient still qualifies. Federal spousal impoverishment protections exist to keep a community spouse from being left destitute when the other needs institutional care, but the rules are complex and do not always prevent eligibility disruptions.4Medicaid.gov. Spousal Impoverishment Marriage to someone with significant income or assets could jeopardize coverage that pays for medical care or long-term services.
Wills and Powers of Attorney
Marriage can disrupt an existing estate plan. In a majority of states, getting married partially or fully revokes a will executed before the marriage. The new spouse may be entitled to an intestate share of the estate, even if the prior will left everything to children or other family. Some states that have adopted versions of the Uniform Probate Code limit the new spouse’s share when the will already provides for children from a prior relationship, but the rules vary widely.
Powers of attorney raise a different problem. Marriage does not automatically revoke a durable power of attorney, but it creates competing interests. If the person previously named a child or sibling as their agent, the new spouse may have grounds to challenge that authority or seek appointment as guardian or conservator. The spouse’s standing as next of kin often gives them priority in guardianship proceedings, potentially displacing the person the family had chosen. A single ceremony can rearrange who controls the person’s finances, who inherits their property, and who makes their medical decisions.