Wilshere had been a free agent after terminating his contract with West Ham United back in October.
The 29-year-old had been training with Bournemouth for the past three weeks to prove his fitness and has done enough to impress manager Jason Tindall.
Wilshere had a loan spell with Bournemouth in the 2016/2017 season, making 27 appearances as the Cherries finished 9th in the Premier League.
"It feels great to be back and I can't wait to get started," Wilshere told afcbTV.
"From the minute I walked through the door three weeks ago, it felt natural and like I had never been away.
"I know a lot of the players and staff here and I'm pleased they allowed me to train initially, and then it just went from, there.
"I've been impressed by the coaching staff, the way they work and the ambitions of the club to get back in the Premier League.
"We all share the same ambitions and I'm looking forward to playing my part in helping achieve those."
Wilshere has won 34 caps for the England national team but it has been more than four years since his last international appearance.
Bournemouth, who were relegated from the Premier League last season, are third on the championship table, eight points behind leaders Norwich City.
