The deal, which was confirmed on Tuesday, has been struck with a view to taking the Frenchman to Ewood Park on a more permanent basis in the new year.
The 25-year-old has been utilised mainly as a substitute since arriving in South Wales from Metz in 2011, with 48 of his 63 appearances coming from the bench.
Nevertheless, the Benin international has managed to score nine goals for the club and started the 2012 League Cup final, which Cardiff lost on penalties to Liverpool.
Subject to international clearance, Gestede could be in line to make his Blackburn debut in Saturday's Championship clash with Leeds United.
Jordan Rhodes is currently Blackburn's top goalscorer in the league with 10.
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