The former international moved to Linfield last summer but he had limited game time at Windsor Park because of injury and was eventually released.
Clingan's cross-channel career included spells at Norwich City, Coventry City, Nottingham Forest and Kilmarnock.
The midfielder, who won 39 Northern Ireland caps, lined out for Glenavon in a pre-season friendly against Loughgall on Saturday.
Glenavon open their Irish Premiership campaign with a contest away to Warrenpoint Town on Saturday.
Glenavon have signed ex-Northern Ireland midfielder Sammy Clingan.