Shearman & Sterling said Wednesday that it will stay put at its longtime Manhattan address for the next two decades and plans to give the space an “innovative and eco-friendly” facelift over the next three years.

The firm said it had signed a 20-year lease for 338,000 square feet at 599 Lexington Ave., a 47-story Boston Properties building at the intersection of 53rd Street that has been Shearman’s home since the 1980s. Its decision to remain in the Midtown East area contrasts with moves by other big firms to new office towers in the Hudson Yards neighborhood on Manhattan’s West Side.