The 28-year-old, who scored three goals in 22 appearances for previous club Charlton last season, has agreed a three-year contract at Griffin Park.
"We are delighted to finally get Paul. It was a long battle to get him," said Uwe Rosler, the Brentford manager.
"Without Paul's commitment and desire to want to play for Brentford, the deal would not have happened.
"It is fantastic to see a player like Paul prepared to make sacrifices to join us and it is pleasing for me that he believes in what we want to achieve. I know that Paul wants to join us for the right reasons and I thank him for that.
"I always said I wanted more experience in the squad and we now have three experienced strikers. There will be good competition for places."