Saracens have recruited Campbell, a member of Britain's victorious 4x100m relay team at the 2004 Athens Olympics, to work with the squad through the season.
Campbell will focus on developing the players' power and speed as Saracens look to build on their Premiership triumph last year by making a mark in the Heineken Cup.
"My job is just to try and sprinkle some magic dust and get that little bit more out of the players, especially those coming back from long-term injuries," said Campbell.
"Over the last few years I've gained more knowledge of rugby and know that speed and explosive power has become a lot more important. Any difference that I can make here would be absolutely fantastic.
"The coaches here are very knowledgeable and it's a fantastic set-up and a fantastic club - I've been very impressed with what I've seen."
Campbell, the former European and Commonwealth Games champion, took his first session with the squad at Old Albanians on Monday.
Saracens high performance director Scott Murphy said: "For us to get to the next level in the Premiership and Europe, we feel we need to develop our power and speed and we want to tap into Darren's knowledge and enthusiasm to drive us to that level.
"He joins us with a terrific track record and will be a valuable resource for the club."
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