Is an IRS debt a separate or joint responsibility of a married couple if the debt was incurred before the marriage?

The pre-marriage debt is separate. However, joint accounts may be liable for it. Here's why. Assume joint account has $1,000. IRS take debtor spouse's half. That leave $5000. It is still jointly owned. IRS can take. In effect, IRS can take the whole thing. But separate property that is kept separate cannot be taken, whether or not the spouses file a joint return for a later, married, year. Still, if the savings for filing joint is not high, and the cost of preparing separate returns is not too high, then you might consider filing separate returns. You can switch to joint any time within 3 years. (But you cannot switch from joint to separate, ever.)

A federal income tax debt incurred by one of the spouses prior to marriage, will continue to be collected by IRS following the taxpayer's subsequent marriage if the couple files a Joint return. To avoid this outcome, the couple should file Married Filing Separately in the future.

There are some differences of opinion on this. The IRS may attach the entire refund because one spouse had a prior debt or it may only attach the portion of the refund belonging to the obligated spouse. The best way is to file married jointly to claim all of the deductions and credits and then file an claim for innocent spouse to protect the non owing spouse.