"My roots in local government are deep," McAdams said. "I really enjoy working at the grass-roots level where the rubber meets the road and interfacing with people and making a difference in people's lives."
His candidacy creates a showdown for the Democratic nomination between two of the party's most prominent members McAdams and Senate Minority Leader Ross Romero.
Mayor Peter Corroon, a Democrat, has said he will not seek re-election.
Romero, a fellow Salt Lake City Democrat, declared his candidacy for mayor in September and said he never expected opposition from McAdams
"I didn't see this coming and obviously I am a little disappointed," Romero said.
Romero said he decided to run for county mayor to avoid an interparty fight with fellow Sen. Pat Jones, whose Senate district was combined with Romero's during redistricting.
Early on, Romero said, McAdams encouraged him to run for mayor and helped him strategize although Mcadams says that is not the case. It wasn't until later that Romero says he heard from other Democrats that McAdams was exploring his own mayoral bid.
"I never envisioned that Ben would be interested in this position because he has been such an advocate for Salt Lake City and many times taken positions contrary to Salt Lake County's interests," Romero said.
McAdams said he didn't decide to run for the race until Romero was in, but he believes voters want alternatives.
"We don't choose mayors based on the first person to throw their hat into the ring," McAdams said. "No political party is a favorite in this race. Politicians certainly don't like competition, but I think competition is good for voters and people like choices."
On the Republican side, Salt Lake County Recorder Gary Ott recently announced his candidacy. County Councilman Richard Snelgrove is considering a bid, as is West Valley City Mayor Mike Winder, who admitted this week to writing pieces for the Deseret News under a fictitious identity.
McAdams said students in Salt Lake Valley schools shouldn't have to stay inside for recess because of health risks due to poor air quality. He said the county can work with cities to develop mass transit and manage growth to reduce pollution from cars.
"Pollution doesn't stop at a city boundary, so improving our air quality is going to take the concerted effort of all 17 municipalities" in the county, he said.
McAdams said he also wants to work with the state to encourage businesses to grow in the valley and believes the county can partner with school districts to develop mentoring programs and supportive communities for schools.
McAdams was chosen by Democratic delegates to replace Sen. Scott McCoy in 2009 and was elected to his first four-year term in 2010.
He also teaches at the University of Utah law school.
As a senator, McAdams played a key role in helping protect Salt Lake City's domestic-partnership registry and, after helping persuade LDS Church officials to support the city's anti-discrimination ordinances, worked to stave off efforts by conservative lawmakers to override the city's practices.
"My reputation is as someone who is collaborative and moderate," he said, noting that he spent hours in meetings on the discrimination ordinances held in the living room of then-Sen. Chris Buttars, a leading social conservative. "My style is to have honest conversations and be fair-minded."
He helped secure funding for the light-rail route to the airport, and he passed legislation to help stop predatory investment schemes and securities fraud.
McAdams said he will continue to serve in the Legislature while campaigning for mayor and is working on legislation to improve funding for schools.
Born in West Bountiful, McAdams served an LDS mission in Brazil, graduated from Columbia Law School and practiced securities law at a prestigious New York City law firm. He worked on President Bill Clinton's advance team ensuring presidential travel runs smoothly and has done similar work for Hillary Clinton, Sen. John Kerry and President Barack Obama.
"What I would hope to bring is my strong bipartisan relationships at the state level ... as a benefit to the county," McAdams said.