I am listed as his wife on the 401k. What are my rights under common law marriage and how to prove it.

What state do you live in? And is your concern regarding your rights if you were to split up? Or your rights if he were to die?

People list a beneficiary of a 401(k) not necessarily a spouse. If that's the case, then it doesn't matter whether you are a spouse if he should die. However, in case of a divorce that might be a different matter.

ScottGem - that's not quite right. If the 401(k) account owner is married federal law requires that the spouse be the primary beneficiary unless the spouse signs a written waiver. Of course this applies only if the marriage is legal, which is why I asked what state the OP lives in, as not all states recognize common-law marriage. Actually what I should have asked is where they were living at the time that the common-law marriage was entered into, and to confirm that they met all requirements of that state to ensure that the common-law marriage is real. It's crtitical to the OP that these requirements have been met to avoid the risk of a court later on deciding that the marriage wasn't really a marriage.

On a side note - if the couple ever decides to split up they must go through a legal divorce just like any other married couple (i.e. there is no such thing as "common-law divorce"), and it's during those legal proceedings that the OP can secure a portion of her former spouse's 401(k) assets.

As I recall 401(k)s were not subject to the guaranteed spousal benefit like defined contribution plans. So either that was changed or my memory is faulty. Could be either. So thanks for clarifying.

I think it's been a rule all along. Here's an interesting article about a man whose wife died, so he named his children as his 401(k) beneficiaries, then later he got remarried and died 6 weeks after the wedding. The court ruled that his entire 401(k) had to go to the new wife, leaving the children disinherited, becase she had not signed a waiver. Ouch!

http://www.investmentnews.com/article/20110515/reg/305159996#