Liability to new spouse

What is the name of your state? Michigan
My fiancee and I are planning to get married soon, but he
has a debt to the IRS that is quite large. If we marry, and
buy a home together, would I be liable for his past debt
of taxes that are owed on a business that he once had?
I now own a home with a large equity and we would like to
buy home together. Could the IRS attach a lien if we owned
a home together, for taxes he owes?

Yes. Do not marry him until the debt is paid off. He should consult a tax attorney about whether an offer in compromise is feasible. If he's married when he tries to make an OIC, your income will be considered when the IRS determines how much he can pay.