The central defender has put pen-to-paper on a two-and-a-half-year deal through to June 2018.
The move sees Ward reunited with Rovers boss Paul Lambert after the pair enjoyed a successful spell together at Norwich City.
"It has been a busy few days to try and get it done, but I'm really pleased and I can't wait to get started training and crack on," Ward told Rovers PlayerHD
"I'm looking forward to putting on the shirt and hopefully being involved.
"Paul Lambert demands standards and he definitely brought mine up a few notches at Norwich and that's something I want to get back to on a regular basis."
Harrow-born, Ward started out at West Ham United, coming through the ranks at Upton Park to play his part in the Hammers' promotion to the Premier League in 2005 with a Wembley play-off final win over Preston North End.
Opportunities were limited for the defender in the top flight, but he enjoyed a loan spell with Plymouth Argyle before signing for Coventry City in a £1m move in June 2006.
Ward spent four seasons with the Sky Blues, making over 120 appearances, and following short stints with Doncaster and Preston, he signed for Lambert's Norwich City on a free transfer in the summer of 2010.
His first year with the Canaries saw him make 39 league appearances as they clinched promotion to the Premier League, but injury prevented him making his top-flight debut until February 2012.
Following six months on loan at Nottingham Forest, Ward joined Bournemouth on a permanent deal in 2013.
The defender made 28 appearances during a two-and-a-half-year spell at the south-coast club and spent time on loan with Huddersfield Town earlier this season.
Ward, who turned 31 yesterday, becomes the second player to join from the Premier League today following the arrival of striker Danny Graham from Sunderland this morning.