Eagan was raised Roman Catholic, but attended public school. Eagan attended Smith College her freshman year, then transferred to Stanford University in Palo Alto, California, majoring in American Studies.
Foreign many years she was a columnist for the Boston Herald. She began writing stories as a child, and was encouraged by her English teacher at Durfee High School in Fall River. After graduation from Stanford, Eagan took a job at the Fall River Herald News at a compensation rate of $15 per story.
She was soon also freelancing for the New Bedford Standard-Times and The Boston Globe.
At 24, she was hired as a full-time feature writer at the Burlington Free Press in Vermont. She returned to New Bedford a year later to become a columnist at the Standard-Times.
In 1981, Eagan was hired as a general assignment reporter at the Boston Herald, and was given a column in 1984. She served a "refining stint" as a senior writer at Boston Magazine, and returned to her column at the Herald, where she wrote regularly until July 2014.
She will write a column about spirituality and devotion to God.
Eagan also co-hosted the Jim & Margery Show with Jim Braude on Boston"s FM 96.9 WTKK. The show ended when that station flipped to an urban contemporary format on January 2, 2013. The team is now broadcasting on weekdays as Boston Public Radio on WGBH Radio, a Boston National Public Radio station.