O'Malley Dillon's great-grandparents were Irish Catholic immigrants from Gorumna Island, County Galway.[5][6] Born in the Jamaica Plain neighborhood of Boston, she has three siblings. Her parents are Kevin O'Malley, a school administrator, and Kathleen O'Malley.[7] When O'Malley Dillon was a child the family relocated from Jamaica Plain to Franklin, Massachusetts, to be closer to her father's job.[7]
O'Malley Dillon attended Tufts University, where she majored in political science and was captain of the university's softball team.[7] In 1998, she earned her bachelor's degree.[8][9] O'Malley Dillon decided she wanted to work in politics while on a family vacation to Washington, D.C.[7]
After the 2016 United States presidential election, O'Malley Dillon chaired the Democratic National Committee's Unity Reform Commission. In 2019, she was involved in an effort by Democratic Party data and political personnel to create a data exchange to allow for greater information sharing between Democratic campaigns and allies, a project that party leaders see as crucial for catching up with the Republican data program.[11] Later in 2019, she was hired as manager of Beto O'Rourke's 2020 presidential campaign.[8][9][12]
In April 2020, O'Malley Dillon was announced as the new manager for Biden's 2020 presidential campaign. She succeeded Greg Schultz and Anita Dunn, who had shared campaign management duties for the previous month and remained with the campaign as senior advisors.[11] O'Malley Dillon was the first person to serve as Biden's campaign manager who was not related to him. Biden's sister, Valerie Biden Owens, had served as Biden's campaign manager for all his previous campaigns, but only served in a senior advisory role in his 2020 presidential campaign.[14] On November 16, 2020, it was announced that O'Malley Dillon would assume the role of White House deputy chief of staff in the administration.[15][16]
In January 2024, it was reported that O'Malley Dillon planned to leave the White House to become Biden's 2024 reelection campaign chair.[17]
On July 1, 2024, O'Malley Dillon told members of the Biden campaign's National Finance Committee that Biden is "probably in better health than most of us".[18]
O'Malley Dillon is married to Patrick Dillon. They have three children. Her second cousin, Matt O'Malley, served on the Boston City Council from 2010 to 2022, and served as its acting president for most of 2021.[7]
^Christmas, S. A. (June 10, 2014). Vice President for Legal Investigations letter complaining of violations of the FEC Act by Obama for America, etc. [Letter written January 8, 2014, to Office of General Counsel, Federal Election Commission]. Retrieved November 17, 2020, from https://www.fec.gov/files/legal/murs/6772/15044380595.pdf