Lyons will join the agency in January as a partner following nearly two years at Tetra Strategy, which he joined in the wake of the closure of the News UK-owned Sunday tabloid in 2011.
In his role as head of media at Tetra Strategy, Lyons led the media campaign against government plans to introduce a minimum unit price for alcohol.
Before this, his fifteen-year career in journalism included five and a half years at the News of the World and seven years at the Press Association.
Tim Collins, chairman of Bell Pottinger's political practice, said: "Jamie brings an insider's knowledge of the Parliamentary lobby. Political journalists are the most likely to secure prominent coverage for their stories.
"Jamie's experience and insight into the workings of the lobby will help our clients navigate the most influential group of journalists on Fleet Street."