[5] The oldest girl in a family of 10 children,[1][4] she attended Marian High School in Bloomfield Hills, Michigan.

[7] She earned her bachelor's degree from Michigan State University in 1979, majoring in urban planning and labor relations.

[9] When a member from the United Auto Workers suggested that the way to end hunger was to enable people to obtain well-paying jobs, Henry began considering union organizing.

[4] She remained active in the union's health care organizing, however, representing SEIU in its talks in 1999 to secure a card check agreement with the Catholic Healthcare West hospital chain.

[4] In her first 25 years with SEIU, Henry played a major role in organizing drives at Beverly Enterprises, Catholic Health Care West, Tenet Healthcare, and HCA, Inc.[5][8] Stern relied on her to coordinate and lead important legislative efforts.

[29][31] "Mary Kay's greatest strength is her ability to build consensus and create a highly effective team around shared goals and responsibilities.

[8] The e-mail also cited the need "to return to organizing as our top priority" and "to restore our relationships with the rest of the union movement and our progressive allies.

"[32] Twelve days after Stern's announcement, national media reported more local unions representing more than 60 percent of SEIU's 1.9 million members had agreed to support Henry's candidacy.

[23][32] But Burger's backers countered that Henry had never led a local union, had little on-the-ground organizing experience, and had associated with many SEIU staff and elected leaders tainted by recent scandals over financial impropriety.

[33] In a memo sent to SEIU leaders nationwide, Henry said, "Our local unions and divisions should drive our national priorities, not the other way around.

[30][34] Mary Kay Henry was elected President of SEIU by the international union's executive board on May 8, 2010, to serve the two remaining years of Stern's term.

[5] However, she said she did not foresee bringing SEIU back into the AFL-CIO and refused to end the union's battles with its breakaway California locals.

[5] A few days after her election, Henry began conducting a review of the duties and assignments of SEIU's top leadership and staff (including Secretary-Treasurer Burger), noting, "It is the prerogative of the president to reassign responsibilities.

[1][5][8][15][30] She and her partner, Paula Macchello (a senior strategic organizer with the International Brotherhood of Teamsters), are both advocates for same-sex marriage.