Global management-consulting giant McKinsey & Co. is moving its Manhattan headquarters from 55 E. 52d St. to Three World Trade Center, The Post has learned.

The deal — kept so under wraps that not even word of negotiations seeped out — is a Thanksgiving present for developer Larry Silverstein. It’s also a gift to the thriving downtown office scene, which boasts a healthy mix of media, creative and traditional financial firms.

But it’s another loss for East Midtown, where the effects of recent rezoning to allow large new modern buildings to rise might not be felt for years.

Although fine points of the lease have yet to be worked out, McKinsey executives were told of the planned move in a memo last week. Many employees were treated to a walk-through of their new home.

Sources said that McKinsey will take about 200,000 square feet on floors 60 to 64 of 80-story Three World Trade Center, including a 5,000-square-foot, south-facing outdoor terrace on the 60th floor.

Once the 15-year lease is signed, as is expected, McKinsey will join GroupM at the Richard Rogers-designed tower.

The building is to open in May. The lease would raise office occupancy to 900,000 square feet in the 2.5-million- square-foot tower.

Terms were not known, but office asking rents at 3WTC have been reported in the $80s per square foot.

McKinsey has some 14,000 “consultants” in 120 cities around the world. The Manhattan office, which it will leave behind, is the firm’s largest, with more than 900 executives.

Silverstein declined to comment, and reps for McKinsey couldn’t immediately be reached.