Brennan is a native of Pottsville, Pennsylvania. She attended Nativity BVM High School, where she played basketball on the 1978 state championship team and played softball. She graduated in 1980 and went to Immaculata College outside Philadelphia. She graduated from there in 1984 with a B.A. in history.
No one can accuse Brennan of taking the easy road to the top. She began with the Postal Service in 1986 as a letter carrier in Lancaster, Pennsylvania. She subsequently worked her way up the ladder as a delivery and collection supervisor, processing plant manager in Reading and Lehigh Valley, Pennsylvania, and a district manager in Springfield, Massachusetts.
Brennan stepped away from the Postal Service for a year to study as a Sloan Fellow at the Massachusetts Institute of Technology. She earned her MBA in 2003.
She served as manager of field support and integration, manager of operations support for the Northeast Area and in May 2005 was named vice president for the Northeast Area, where she coordinated and integrated processing and distribution, transportation and delivery operations in that region.
Brennan was then named vice president of Eastern Area Operations, putting her in charge of postal operations in Pennsylvania, Ohio, West Virginia, Delaware, Kentucky, Central and South Jersey, Western New York and parts of Virginia and Indiana.
In December 2010, Brennan was named chief operating officer and executive vice president of the Postal Service. Beginning in 2012, she had to begin shutting mail-handling facilities because of budget cuts brought on by less mail and Congressional-mandated pension funding rules. Initially many rural post offices were on the chopping block as well, but outcries from affected residents, as well as their representatives in Congress, forced another plan. Instead, hours in many rural facilities were cut, but the offices were saved.
Brennan wasn‚Äôt the only postal worker in her family; her late brother worked in the hometown Pottsville post office until he died in 2013