A native of Washington, DC, McCartney attended Georgetown Visitation Preparatory School.
She graduated from Boston College in 1994 and received a master's degree in curriculum and instruction from the George Washington University.
Before starting SBP, McCartney was the Executive Director of a community-based nonprofit organization in Washington, DC which provided technology-based after school and summer programs for young people attending DC public schools.
McCartney and Zack Rosenburg volunteered in St. Bernard Parish in March 2006 after the storm.
They then quit their jobs in Washington, returned to Louisiana in June 2006, and the following August they cofounded the St. Bernard Project.