McCrummen, granddaughter of former Judson College chancellor Norman McCrummen, graduated from Ramsay High School in 1988. She completed her bachelor's degree at the University of North Carolina Chapel Hill in 1992 and a professional degree from Columbia University's Graduate School of Journalism in 1998. During her college years, she worked as a community organizer, as an intern for Pacifica Radio, and as a secretary at the World Bank. After completing her degree, she took a reporting job with Newsday, where she covered government, development and the Long Island region,
McCrummen moved from Newsday to The Washington Post in December 2004. She initially reported from the DC suburbs, then succeeded Emily Wax as the paper's East Africa bureau chief in Nairobi, Kenya for three and a half years beginning in September 2006. In her career, she has also reported from Egypt, Iraq, and Mexico. She is currently a member of the paper's national enterprise team.
McCrummen was awarded the 2015 "Erikson Institute Prize for Excellence in Mental Health Media" for her numerous feature stories involving people experiencing mental illness. She was the lead reporter for a November 8, 2017 exposé in the Washington Post described the experiences of young women claiming to have been sexually assaulted or harassed by U.S. Senate candidate Roy Moore. The paper was awarded a "Pulitzer Prize for Investigative Reporting" for that story.