The 35-year-old defender made one appearance for Rovers in 2001 after joining from Clyde, before moving to Kilmarnock in 2003.
Greer was released by Brighton in May after their play-off semi-final loss to Sheffield Wednesday, having made 234 appearances in six seasons.
The ex-Swindon and Doncaster centre-back has won 11 caps for Scotland.
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Blackburn Rovers have signed former Brighton captain Gordon Greer on a one-year deal.