Service Employees International Union, a key White House ally in the 2008 presidential campaign and the recent health care debate, elected its first female president on Saturday.

In Washington, D.C., SEIU board members chose Mary Kay Henry as the successor to Andrew Stern. Stern abruptly announced his departure last month after running the union for nearly 15 years. Until Saturday’s vote, Henry was an executive vice president with the organization.

“This moment marks a renewed commitment to our union’s core mission: to improve the lives of all workers who are struggling to make ends meet in this economy,” Henry said in a statement. “Working people are facing hardships we haven’t seen in generations, and we believe SEIU can be an even more effective vehicle for change to help them improve their lives and the lives of the people they serve.”