Hahnemann has signed a contract with the Toffees until January after being released by Wolves in the summer.
The 39-year-old - holder of nine caps for the United States - will provide back-up at Goodison Park to compatriot Tim Howard and Jan Mucha.
Everton boss David Moyes said: "It is difficult when you only have two senior goalkeepers - it only needs one of them to go down and then you are in trouble.
"Marcus is friends with Tim. It is after the transfer window has closed and we had to look for someone who we knew.
"I would have liked to have got somebody before the window closed if we could, but there were other priorities at the time.
"It gives me someone who can help in the reserves and if we get an injury to a goalkeeper, he has got good experience of the Premier League and we can use him as back-up."
Hahnemann arrives at Everton following a two-year spell at Molineux and he previously played in the Premier League with Reading.
Source: Team Talk
Source: Team Talk