The company, Blackstone, which Mr. Schwarzman helped found, said on Saturday that Saudi Arabia’s sovereign wealth fund had committed $20 billion to a new investment fund aimed at infrastructure projects, primarily in the United States.

The commitment is about half of the capital Blackstone plans to raise for the fund. All told, including potential borrowed money, the new fund could invest more than $100 billion in infrastructure projects, the company said in its statement.

The fund was one of several business deals between an American company and Saudi Arabia announced after Mr.

And the Trump administration helped line up $110 billion worth of arms deals, negotiations in which senior officials played prominent roles. For instance, Jared Kushner, Mr. Trump’s son-in-law, personally called the chief executive of Lockheed Martin to cut the price of a radar system.

In its statement on Saturday, Blackstone said it had begun discussions with Saudi Arabia about a year ago. The American investment company said it had already invested in over $40 billion worth of projects tied to infrastructure over the last 15 years.

Investing in American infrastructure has been advocated by lawmakers and business leaders for some time, with both Mr. Trump and Hillary Clinton endorsing modernizing aging airports, bridges and energy systems through public-private partnerships.

For Saudi Arabia, the new fund is yet another step toward diversifying its enormous oil-based economy. The kingdom has already announced what it calls its Vision 2030 plan, under which the country has prepared to list its state-owned oil producer, Saudi Aramco, on the public markets.

Earlier on Saturday, the Japanese telecommunications giant SoftBank announced the first end of the first round of fund-raising for its Vision Fund, a planned $100 billion technology investment vehicle to which the kingdom had pledged $45 billion.