What would be the advantage of such a move?
I don't see any.
The disadvantages would be numerous
1) Your credit rating would be shot.
You would not be able to borrow for a car or for any other purpose for at least 5 years.
2) If things get really bad, you would become liable for the full mortgage or both would have to avail of one of the insolvency measures
At the moment, if things get really bad, your partner can go bankrupt or avail of a PIA. You would not be impacted.
If you are both on the mortgage, and he becomes insolvent, you become liable for the full mortgage, and not just half of it.
3) If you split up, you will find it almost impossible to get a mortgage in your new life
Many relationships end.
If yours ends and let's say you start a new relationship with someone else.
You decide to buy a house together but you will not be able to borrow because you already have a mortgage - whether it's in arrears or not.
4) If it's in positive equity you would have to pay gift tax as you are not related.
Presumably you want your name on the title deeds and not just the mortgage?
Let's say that the house is worth €350k and the mortgage is €200k
The equity is €150k
You would be deemed to have received a gift of €75k
The first €15k would be exempt
So €60k would be taxable at 33%
You would have to pay Capital Gains Tax of €20k.
Brendan