Microsoft has signed a downtown lease for a major office outpost in New York City, The Post has learned.

The tech giant this week signed its lease for about 70,000 square feet of space with the new owners of 300 Lafayette St., who have just closed their $125 million purchase of the newly developed, 11-story office tower located on the south side of Houston Street, sources said.

Another 8,500 square feet of retail is still available in the building, according to people close to the deal.

Designed by CookFox Architects to maximize light and air, 300 Lafayette has floor-to-ceiling windows, with terraces and greenspace on nearly every floor, and is surrounded by distinctive railings.

The building’s developers, Related Cos. and LargaVista Companies, contracted to sell the project to Nightingale Properties and Wafra Capital Partners in 2017 while it was under construction. The same buyers are also in contract for 711 Fifth Ave. for $907 million.

The building is on a long-term ground lease on land owned by LargaVista on the site of the former BP gas station, opposite the Puck Building.

The project was marketed by Dustin Stolly of Newmark Knight Frank along with Clark Finney of JLL. Finney also represented the buyers on the office lease with Microsoft, which was repped by JLL colleague Lisa Kiell. The brokerages declined to comment.

The $145 million acquisition financing was arranged for the buyers by an NKF team led by Stolly and Jordan Roeschlaub along with Nick Scribani, Chris Kramer and Dylan Kane. The loan was provided by TPG Real Estate Finance Trust and will enable the buyers to complete tenant installations and other items.