In an email to supporters, Brown said he chose to run for office again after he decided he "still had something to give back to our community."
"The stakes are high in Washington, but they're even higher for hard-working families right here in Prince George's and Anne Arundel Counties," according to the email. "I know this isn't going to be easy, but nothing worth fighting for ever is."
Brown, a Mitchellville resident, entered the race a day after former State's Attorney Glenn F. Ivey said he, too, will jump in -- setting up what could be one of the state's most closely watched Democratic primaries in the 2016 election.
Brown, 53, ran an unsuccessful campaign for governor last year, losing to Republican Gov. Larry Hogan in the general election. But the Democrat performed better in Prince George's County than any other in the state and likely has high name recognition after spending millions on television advertising in the Washington media market.
In 2014 Brown beat Hogan in Prince George's County with 84 percent of the vote there, but he also received fewer votes than other Democratic candidates in the county -- including County Executive Rushern L. Baker, III and Comptroller Peter Franchot.
Brown did perform well in the primary in the county, capturing 51 percent of the vote compared with 24 percent for former Attorney General Doug Gansler and 22 percent for Heather Mizeur.
Born in New York, Brown served five years as an Army helicopter pilot. He completed his active duty in 1989 as a captain and remained in the Army Reserve until last summer. After attending Harvard Law School, where he was a classmate of Barack Obama's, he moved to Maryland and took a job with a Washington law firm.
In 1998, still a relative newcomer to Maryland, he won a seat in the House of Delegates from Prince George's County.
He served as lieutenant governor, in former Gov. Martin O'Malley's administration, from 2007 until January.
Brown's entrance into the race sets up something of a familial rematch: Ivey's wife, former state delegate Jolene Ivey, ran as a lieutenant governor candidate against the Brown ticket in the Democratic gubernatorial primary last year. Brown ultimately won the nomination but lost to Hogan in November.
Brown's name had been floated as a possible candidate for Senate when longtime Sen. Barbara A. Mikulski last week announced her retirement, but the idea met with some push back from state Democrats who quietly suggested it was too soon for Brown to run statewide after such an upset loss.
But many of the factors that plagued Brown in the gubernatorial race -- the failed launch of the state's health care website, the relatively low turnout in a strong year for the GOP, an electorate that some polls suggested had grown weary of Democratic control in Annapolis -- would likely be much less of a factor in the 4th Congressional District contest in 2016.
The district is based in Prince George's County but includes a large swath of Anne Arundel County as well.
Brown still owes several hundred thousand dollars in a loan he took from the Laborers International Union at the end of his campaign last year. His fundraising for federal office would flow into different accounts than were used for his statewide campaign.