The 29-year-old arrives at the Madejski Stadium as injury cover for Nic Rouse.
"Dave is a physical, ball-carrying second-rower who has amassed plenty of experience in the Premiership," director of rugby Brian Smith told the club's official website. "There is plenty of rugby to play in the next couple of months so Dave will get an opportunity."
London Irish are currently in ninth place in the Aviva Premiership table after taking 12 points from their first six games of the season.
The Exiles return to action on Sunday when they host Italian side Rovigo in the European Challenge Cup.