BOSTON — Tom Ryan, former chairman and chief executive officer of CVS Caremark Corp., has joined the Operating Partner Program at private equity firm Advent International.

Advent said Thursday that Ryan will advise and work closely with its investment professionals to identify "attractive opportunities and generate post-investment value at retail and health care companies globally."

"Advent has a proven ability to tackle complex situations and deliver long-term value through operational enhancements and earnings growth, even in low-growth environments," Ryan said in a statement. "I am delighted to join a firm with a solid track record of success. Advent is a highly focused global organization, and I’m excited to now be part of the team."

Ryan retired as CVS Caremark chairman in May and was succeeded as CEO by president and chief operating officer Larry Merlo in March.

Joining CVS in 1974 as a pharmacist, Ryan rose up the ranks through a series of senior positions, becoming CEO in 1994 and adding the title of chairman in 1998. He oversaw the transformation of CVS Caremark from a drug store chain focused on the northeastern United States into a comprehensive pharmacy services company, with a national footprint and revenue of about $100 billion in 2010. Advent noted that CVS Caremark has achieved strong revenue and profit growth, with its market capitalization growing from $4 billion in 1996 to almost $50 billion last year.

"Tom is simply one of the world’s top corporate leaders. He is tireless in his pursuit of new ideas, innovation and growth," stated David Mussafer, managing partner at Advent. "That drive, combined with his expertise in the retail and health care sectors, complements Advent’s time-tested approach to value creation. He is a great addition to Advent, and we look forward to working with him to identify and develop investment opportunities on a global basis."

Ryan currently serves on the board of directors of Yum! Brands and previously has served on the boards of Bank of America and Reebok International, Advent added.