State representative

In 1990, Lambert was re-elected, defeating Republican Thomas Costello and again defeating former Representative Charles Silvia (running as an Independent) with over 73% of the vote.^[7] He was re-elected in 1992 and 1994 without opposition.^[8]

Mayor of Fall River

In 1995, Lambert entered the race for Mayor of Fall River, after incumbent Mayor John R. Mitchell decided not to seek reelection. Following the September preliminary, Lambert defeated former City Councillor Cathy Ann Viveiros with almost 65% of the vote in the November election.^[9] He was re-elected in 1997 against token opposition, and defeated City Council President William F. Whitty (who would succeed him as Acting Mayor) in 1999. In 2001, he was re-elected to a fourth term against local restaurateur Paul R. Viveiros, which centered largely around the latter's attempt to operate an adult entertainment club within city limits, which was opposed by city government.^[10][11][12] Lambert's most narrow win came in 2003, winning by only 903 votes against local Portuguese language translator, F. George Jacome, who was seen as having stronger ties to that large constituency. After a term of outreach, as well as added support due to his fight against attempts by Hess Corporation to locate an LNG facility in the city, Lambert defeated Jacome with 61% of the vote in a rematch of their previous race.^[13]

In 2007, Lambert declined to run for reelection, resigning from office on October 26 to take a position as Director of UMass Dartmouth's Urban Initiative. The timing of his resignation was motivated in part by the fact that the Fall River Charter allows for the City Council President (Whitty at the time) to temporarily fill a mayoral vacancy. As Whitty was a candidate for mayor, the potential of his serving as mayor was considered an unfair advantage by Lambert, though this was moot after Whitty's defeat in the preliminary election.^[14]