Passidomo was born in Jersey City, New Jersey, and attended Trinity Washington University in Washington, D.C., graduating with a Bachelor's degree in 1975, and later graduated from the Stetson University College of Law with a law degree in 1978 after moving to the state of Florida in 1976. She entered into private law practice and started the law firm of Kelly, Passidomo & Alba LLP.
In 2010, when incumbent Republican State Representative Tom Grady declined to seek another term in the legislature, Passidomo ran to succeed him in the 76th District, which stretched from Naples Park to Chokoloskee on the western coast of Collier County. She won both the Republican primary and the general election entirely unopposed.
Following the reconfiguration of legislative districts in 2012, Passidomo was moved into the 106th District, which included most of the territory that she had previously represented in Collier County. In the Republican primary, she was opposed by David Bolduc, whom she easily defeated with 73% of the vote. Advancing to the general election, Passidomo faced Libertarian candidate Peter Richter, whom she defeated in a landslide, winning her second term in the legislature with 79% of the vote.
While in the legislature, Passidomo spoke out in favor of legislation authored by Florida House of Representatives Hazelle P. Rogers in 2011 that required school districts to "adopt a dress code that prohibits students from 'wearing clothing that exposes underwear or body parts in an indecent or vulgar manner. In 2013, she authored legislation that would expedite the foreclosure process in the state of Florida, which would "[shorten] the period of time banks can collect losses from five years to one."
Passidomo has received the following awards while in office:
Elder Law Section of The Florida Bar, Legislator of the Year, 2014, 2015 Trial Law Section of The Florida Bar, Legislator of the Year, 2015 Florida Council on Aging, Advocacy Award, 2014 American Institute of Architects, Florida Legislator of the Year, 2013 Community Advocacy Network, Community Association Legislator of the Year Award, 2013 Florida Bankers Association, Legislator of the Year, 2013 Florida Land Title Association, Legislator of the Year, 2013
In 2016, Passidomo ran for the Florida Senate seat vacated by Garrett Richter, who was term limited. She defeated fellow state representative Matt Hudson in the Republican primary, 58 to 42%, and faced only write-in candidates in the general election.
She is one of the founders of Maggie's List.