The move comes a little more than four months after Ryan was fired by the Twins in the middle of his 19th season. He spent 31 years with the team, starting in 1986 as the scouting director. During his time running the baseball operations department, from 1994-2007 and 2012-16, the Twins won four division titles.
"I'm very happy to be joining the Phillies and have the opportunity to provide some impact and evaluation," Ryan said in a statement. "This is an exciting time for the franchise as they have what many in the industry consider to be one of the top farm systems in baseball."
Ryan's first job in the major leagues was as Midwest scouting supervisor for the New York Mets from 1980 to 1985.
"Terry's work ethic, loyalty and track record as a talent evaluator are simply unparalleled in our game," Phillies general manager Matt Klentak said in a statement.
The Associated Press contributed to this report.