Mr. Townsend and the executive suite will be housed on 42.

But Condé’s highest, and presumably most sought after floor, is going to the company’s law firm, Sabin, Bermant & Gould.

Condé Nast is not the first to move into the trade center towers. Last Monday, the Port Authority of New York and New Jersey began moving into its space at 4 World Trade Center, a 72-story tower built by developer Larry Silverstein that opened last year.

But it was Condé Nast’s decision to leave Midtown in 2011 that turned heads, prompting others to consider the same. Since then, Time Inc., another Midtown stalwart, announced it would be moving nearby, to 225 Liberty Street.

MediaMath, a global technology firm, will join the Port Authority at 4 World Trade, and GroupM, a media and advertising firm, has leased space in Mr. Silverstein’s 80-story building at 3 World Trade Center, which is under construction.

For many years, it was unclear who, if anyone, would move into the trade center buildings given the history of the site. Lehman Brothers fled to Midtown, before disappearing during the financial crisis.

More recently, JPMorgan Chase sold Chase Manhattan Plaza, the downtown office tower, and Bank of New York Mellon sold its Art Deco building at 1 Wall Street. Technology, advertising and media companies have replaced them, taking advantage of lower rents and tax breaks.

Still, the towers are far from filled. One World Trade Center has leased 58 percent of its 3 million square feet of space. Douglas Durst, the developer who is a co-owner of 1 World Trade Center with the Port Authority, expects that Condé Nast will play the same transformational role downtown that it did 15 years ago when the company moved to his tower at Broadway and 42nd Street, 4 Times Square.