The 33-year-old missed Wales' World Cup qualifiers with Scotland and Croatia in the autumn but the former Liverpool man is set to hand his county a real boost by being available for next week's friendly with Austria.
And Bellamy, who has scored four goals in 19 Cardiff appearances this season, will met up with Chris Coleman's squad with the Scot's blessing.
Mackay said: "I want to make sure my players are best prepared for our games. But I've always been a big advocate of players playing international football. It was something I was very proud to do myself.
"I'm delighted when my players are called up for their national teams.
"I spoke to Chris Coleman and he will be delighted that Craig has put himself up for selection.
"I think with his performance levels right now he's going to act as a real boost to the Welsh squad. You always want your best players available."