The 27-year-old forward has been a prolific scorer at League One level in the past but has struggled mightily in the Championship this season, scoring just one goal in 21 outings.
Wright-Phillips was named in the League One team of the season in 2010-11 after scoring 21 times for Plymouth Argyle and Charlton, and he scored 22 more for the Addicks last season in their promotion campaign.
Brentford's sporting director Mark Warburton said: "As we approach the business end of the season, it is very important to keep everything fresh.
"Bradley is a proven goal scorer in this division and is a player we have been looking at for a long time.
"He is a player that was chased by teams in the Championship and some of our rivals for promotion this season, so we are delighted we could secure him.
"We are very pleased to bring him to Griffin Park and hopefully he can help us achieve our aims and ambitions for the season.
"He had an outstanding season in League One last season and hopefully he can continue that form this time around."