Hollywood agency powerhouse William Morris Endeavor is joining the cast at 11 Madison Ave. overlooking Madison Square Park, The Post has learned.

The agency, which represents A-listers from Justin Timberlake and Emma Stone to Hugh Jackman and Charlize Theron, has signed a lease for the full 70,000-square-foot 18th floor.

The 2.3 million-square-foot building, owned by Alex Sapir and Rotem Rosen of the Sapir Organization and the CIM Group, also counts Sony as an incoming tenant, while negotiations with Yelp are underway.

Asking rents in the building are now $92 a foot due to the hot Midtown South market, according to CoStar data, although WME’s long-term deal with expansion options was inked at a lower rent.

Brian Goldman of Newmark Grubb Knight Frank and John Mambrino of Savills Studley represented the tenant in its long search, while Brad Gerla and Howard Fiddle of CBRE worked for the building ownership. All declined to comment.

Eleven Madison is also convenient to modeling agency IMG, which WME and buyout firm Silver Lake recently purchased, and will remain at the nearby 304 Park Ave. South at East 23rd Street.

William Morris, which joined forces with Ari Emanuel’s Endeavor in 2009, has long had its New York office on two floors at 1325 Ave. of the Americas.