The 34-year-old is their first transfer deadline day recruit.
Adam Le Fondre has joined Wigan while goalkeeper David Marshall moved to Hull City as deadline day approached.
However, with striker Federico Macheda having left the Welsh capital, Cardiff also brought in Joe Bennett from Aston Villa. on loan from Bolton Wanderers.
With Lambert joining from West Brom, manager Tony Pulis looks set to plug the gap by signing free agent Hal Robson-Kanu, the Wales striker.
Lambert has scored 214 goals in 589 league appearances since his career began as a trainee at Blackpool in 1998.
Cardiff City have signed England striker Rickie Lambert from West Bromwich Albion on a two-year deal for an undisclosed fee.