The Trinidadian all rounder, flamboyant with the bat and a natural wicket taker with the ball, will bring fresh optimism after their impressive win over Lancashire in the quarter-finals.
With Dutch all rounder Ryan Ten Doeschate likely to be injured and Scott Styris now with New Zealand this is an important capture for Essex.
Bravo will not be the only West Indian on show at the Rose Bowl as fellow compatriot Kieran Pollard will feature for Somerset.
Essex head coach Simon Grayson, was delighted with the deal.
Ã¢â‚¬Å“We see Dwayne as a like-for-like replacement for Scott Styris,Ã¢â‚¬Â he said.
Ã¢â‚¬Å“He is a top-class player and we hope he can make a major impact on finals day.Ã¢â‚¬Â
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BIOGRAPHY: Cesc Fabregas