Emmanuel T. Hernandez, the executive chairman of SunEdison’s board, said on Wednesday that the move “makes clear our unequivocal commitment to SunEdison and its common shareholders.”

He added, “As we work to navigate current market conditions, we are very pleased that we will have the benefit of tapping the expertise of a highly qualified director endorsed by a significant shareholder.”

Last year was a particularly rough one for Mr. Einhorn. Halfway through 2015, it appeared as if SunEdison would be a bright spot in his otherwise beleaguered portfolio of stocks. He called it in a letter to investors “our only significant winner” at the time as the stock moved from $24 a share to $29.91 a share over the second quarter. On Tuesday night before SunEdison announced the change to its board, its stock had closed at $3.05.

In that same letter last summer, Mr. Einhorn urged investors to sit tight and signed off with a quote from the inventor Thomas A. Edison: “A diamond is a piece of coal that stuck to the job.”

A veteran in the hedge fund industry, Ms. Gogel worked for Discovery Technology Fund, and founded a long-short equity hedge fund called Perennial Advisors. She left Greenlight Capital at the end of 2014 “to pursue other interests and spend more time with her family,” Mr. Einhorn wrote to investors at the time.

Mr. Einhorn and Greenlight Capital have had seats on the boards of other companies and he is currently chairman of the board at Green Brick Partners, a real estate operator. But he is perhaps best known for his battle against New Century Financial, the mortgage company. In 2006, after threatening to wage a proxy war and oust three directors from New Century Financial, the company made him a director.

One year later, as the subprime market was imploding and New Century’s stock was plunging, Mr. Einhorn resigned from the lender’s board five days after it disclosed that federal authorities had opened a criminal probe looking into accounting irregularities. A month later the company filed for bankruptcy.

Gaining a seat on the board of a company has not always been a successful move for other hedge fund managers. William A. Ackman resigned from the board of the retailer J.C. Penney in 2013 after a fight over top leadership.