Chairboys boss Gary Waddock told the club's website: "We've been looking at a centre-back after Adam Hinshelwood retired and Bennett fits the bill.
"We know about him and what he will bring to the group."
The Irishman spent six years at Cork City before joining Reading in 2007.
He failed to break into the first-team at the Madejski Stadium and after loan spells at Southampton and Brentford he joined the Bees permanently at the beginning of last season.
Brentford boss Andy Scott told the club's website: "Andy was an integral part of the side that achieved promotion in 2009.
"Unfortunately since then his opportunities to progress have been limited and I think it's in the interest of both parties that we reached an agreement to terminate his contract."
Source: BBC Sport
Source: BBC Sport