The former Tottenham midfielder has been without a club since his contract at Wolves was terminated in August.
O'Hara's three-year spell at Molineux came to an acrimonious end as he fell out of favour - his last appearance for Wolves was during a League Cup tie at Carlisle United in August 2013.
But the 28-year-old has been handed a chance to impress by Blackpool, who are bottom of the second tier of English football, and is determined to make the most of it.
"I'm delighted this opportunity came along, [manager] Lee Clark gave me a call and I jumped at the opportunity," O'Hara told the club's official website.
"I'm desperate to get back on the football pitch.
"I'm really happy to be on board and hopefully I can help the team get some points on the board quickly."
O'Hara could make his Blackpool debut at Leeds United on Saturday.
