Nonetheless, as he immersed himself in the issues, he gradually came around to Mr. Walker’s view that the be-all and end-all of a foundation’s work shouldn’t be to increase the endowment. “If we can invest in ways that support the mission and purpose of the foundation, and still earn a decent return, why not try?” he said. He said he expected these mission-related investments to underperform Ford’s more traditional approach, but nonetheless, “the social good should more than offset that.”

He stressed that Ford had built numerous safeguards into the effort, such as investing the $1 billion in phases. “We’re talking about 8 percent of the portfolio over 10 years,” he said. “After Year 2 or 3, if it doesn’t work, we’ll slow down. If it goes well, we can go ahead even faster.”

His support proved critical for mustering board support. It’s “not a hidebound conservative board by any stretch,” Mr. Nadosy said. Still, “this was difficult. We talked a lot and, quite frankly, it took some work.” (The board includes Gabrielle Sulzberger, who is married to Arthur Sulzberger Jr., the publisher of The New York Times.)

Given Ford’s size and prominence, its move is likely to generate a wave of new mission-related investment. In his letter, Mr. Walker called on endowments of all kinds, including pension funds, sovereign-wealth funds and university endowments, to get on the bandwagon and “help capital markets become accelerators of justice.”

“The Ford move is very significant,” said Jessica Matthews, head of mission-related investment at Cambridge Associates, a large investment advisory firm with many foundation and university clients. Last year, Cambridge surveyed its nonprofit clients, and nearly one-third of those who responded said they were using endowments to make mission-related investments. Of that group, 62 percent said they expected to increase their commitment over the next five years.

Ms. Matthews said that it was too soon and the database still too small to produce a reliable measure of returns, but that “the good news we’re seeing is there are bright spots,” with some social impact investments performing very well.

Not everyone is rushing to follow Ford’s example. “I congratulate them and look forward to seeing how they do,” said Vartan Gregorian, president of Carnegie Corporation of New York, but he said the foundation would adhere to its traditional approach, which has served its mission well over its 106-year history.