Mary Claire Cheney (/ˈtʃeɪni/; born March 14, 1969) is the youngest of two daughters of Dick Cheney, the 46th vice president of the United States and 17th United States secretary of defense, and Lynne Cheney. She is involved with a number of political action committees. She married her wife, Heather Poe, in 2012, and was a signatory to an amicus curiae brief submitted to the U.S. Supreme Court in support of same-sex marriage during the Hollingsworth v. Perry case in 2013.

Cheney was born in Madison, Wisconsin. She attended McLean High School in McLean, Virginia, graduating in the class of 1987. Following that, she attended Colorado College, her mother and sister's alma mater, in Colorado Springs, Colorado, and graduated in 1991. She earned a graduate business degree from the University of Denver in 2002.

In 1993, she became one of the first employees of the Colorado Rockies baseball team, working in promotions when the team began playing in Denver; thereafter, she was a public relations manager for the Coors Brewing Company, and worked as a gay outreach coordinator, helping to end a national Coors strike and boycott by the gay community.

She had been one of her father's top campaign aides and closest confidantes. In July 2003, she became the Director of Vice Presidential Operations for the Bush re-election campaign in 2004.^{[citation needed]}

Cheney was vice president of standards and practices at AOL, leaving in 2007.

Mary Cheney has been with her wife, Heather Poe, since 1992.

Cheney has voiced support for same-sex marriage, and has been credited with encouraging her father's approval of it, which he publicly supported once leaving the vice presidency.

In December 2006, Mary Cheney was reported to be pregnant. She and Poe were said to be "ecstatic" about the baby. "The vice president and Mrs. Cheney are looking forward with eager anticipation to the arrival of their sixth grandchild," spokesperson Lea Anne McBride said on December 5.