Wales international Beard suffered an ankle injury during his countries autumn series defeat against Australia and is expected to be sidelined for three months.
Spencer, 32, arrived in Northampton at the start of the 2024-25 season on a short-term deal from French Pro D2 side Soyaux-Angouleme and has played two games in the Premiership Cup this season.
He has made 76 appearances in the Premiership during stints with Worcester Warriors, Leicester and Bath.
Spencer has been registered in time for the Challenge Cup trip to face Montpellier on Saturday.
After coming through the Bath academy set-up, Spencer made his senior debut in 2013.
Spencer moved to Worcester in 2016, where his 30 appearances across two seasons earned him an international call into England’s squad for a training camp in 2017.
He then switched to Leicester in 2018 where he made 33 appearances before returning to Bath in 2020.
The lock featured in both the Gallagher Premiership and Heineken Champions Cup in his second stint at the Rec, making 42 appearances before heading to France.
Speaking on his move, Spencer said:
“I’m excited to be joining the Ospreys. I’ve heard some great things about the atmosphere at the club, and after some conversations with the coaches, this felt like an easy decision for me.
“The club have a rich history and some quality players in their ranks, and I’m looking forward to playing my part in whatever way I can this season.”
Head coach, Toby Booth, said:
“We’re really happy to have confirmed the signing of Will. He is an injection of real quality in a position we really prioritise.
“He’s got a wealth of experience, and we believe that he will be able to make some real contributions both on the pitch, and on the training ground.”
[Lead image: Ospreys Rugby]
