The South Africa international joins for an undisclosed fee in a deal tying the player to Craven Cottage until the summer of 2011.
The midfielder moves from Golden Arrows where he made 82 appearances since 2005. An agreement has been in place for a few weeks but the 24-year-old had to wait for international clearance before completing the move.
very special
"I am so happy that my transfer to Fulham has been finalised," he told the club's official website. "I have spent most of the summer training with the players and getting to know them and all of the coaching staff.
"I have been given a wonderful chance to be part of a fantastic team playing in one of the best leagues in the world, this is something very special to me and an opportunity that I am going to grab with both hands."
Dikgacoi played in all five of South Africa's Confederations Cup matches this summer and has 28 caps for his country.
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