Short answer: in almost every case, no. Cheating or adultery that happens after you are married is generally not a ground for annulment. An annulment says your marriage was never legally valid in the first place because something was wrong at the moment you married. An affair that started later does not change whether the marriage was valid when it began — so infidelity is normally handled through divorce, not annulment. If your spouse cheated, the legal path you are usually looking for is a fault-based divorce on the ground of adultery (in states that allow it) or a no-fault divorce.
That distinction feels like a technicality when you are hurting, but it controls which case you can actually file and win. Below is what annulment really is, the one narrow situation where infidelity-related facts can matter, and what to do instead.
Annulment vs. divorce: the difference that decides everything
A divorce ends a valid marriage. It accepts that you were lawfully married and now legally separates you. An annulment is different: it declares that a valid marriage never existed, treating it (for most purposes) as if it never legally happened. Because of that, annulment grounds focus on defects that existed at the time of the wedding — not on anything a spouse did months or years later.
Adultery is, by definition, something that occurs during the marriage. So it points to divorce, not annulment. This is the single most common misconception about annulment, and it is why a lot of people who ask for an annulment are gently redirected to a divorce by lawyers and courts.
One more practical note: family law is overwhelmingly state law. The exact grounds, deadlines, and effects of annulment differ from state to state, so treat the categories below as the common framework rather than a guarantee for your state.
What annulment is actually for
States generally allow annulment only when the marriage was either void (invalid from the start, like an illegal marriage) or voidable (valid until a court sets it aside because of a flaw present at the wedding). Typical grounds include:
- Bigamy — one spouse was still legally married to someone else.
- Incest / prohibited relationship — the spouses are too closely related under state law.
- Underage — a spouse was below the legal age to marry without required consent.
- Lack of capacity — a spouse could not consent due to serious mental incapacity, or was intoxicated to the point of being unable to understand the marriage.
- Duress or force — a spouse was threatened or coerced into the marriage.
- Fraud or misrepresentation that goes to the essence of the marriage — a lie so fundamental that the other spouse would never have married had they known the truth.
- Inability to consummate — in some states, a concealed and permanent inability to have sexual relations.
Notice the pattern: every one of these is about something that was already true or already happened before or at the wedding. A later affair simply does not fit.
These rules apply equally to all valid marriages. After Obergefell v. Hodges, 576 U.S. 644 (2015), every state must license and recognize same-sex marriages, and the federal Respect for Marriage Act (Pub. L. 117-228; see 1 U.S.C. § 7) requires the federal government to recognize any marriage valid where it was performed. So the same annulment-versus-divorce analysis works the same way regardless of the spouses' sex.
The one narrow exception: fraud that existed at the wedding
Here is where infidelity-adjacent facts can occasionally support an annulment — but read this carefully, because it is the part people misunderstand most.
Annulment for fraud is not about the affair. It is about a lie or concealment that existed at the time of the marriage and went to the very essence of the marital relationship. A few examples that courts in some states have treated as potential fraud grounds:
- A spouse was secretly pregnant by another person at the wedding and concealed it.
- A spouse never intended to be in a real marriage at all — for example, married only to obtain an immigration benefit or money while concealing an existing relationship.
- A spouse concealed something fundamental that they knew would have stopped the marriage, such as concealing that they were already secretly married to or committed to someone else.
Even then, the bar is high. Generic complaints — “I later found out my spouse was the cheating type” or “they lied about being faithful” — usually are not enough. Courts are skeptical of after-the-fact claims that a spouse “never intended to be faithful,” and what qualifies as fraud “going to the essence” of marriage varies significantly by state. If your situation truly involves a pre-wedding deception, that is a fact worth raising with a local family lawyer — but discovering an affair that began after the wedding does not, by itself, meet this standard.