Conversion to Marital Property

My husband sold some stock in 2013 that he owned prior to our marriage and the proceeds were deposited into our joint account bank account (with right of survivorship). He is now claiming those proceeds are separate property. Didn’t he convert those proceeds to marital property when he deposited them into our joint account?

The way that an account is titled doesn’t really have bearing on whether property is separate or marital. So, simply the act of depositing it in the joint account doesn’t on it’s face mean that it became marital property. You could make the argument that by doing so, however, he gifted that money to the marriage and as such it became marital property.