On February 12, 2010, Lantigua announced that he would give up his seat in the Massachusetts House of Representatives. In a letter to House Speaker Robert DeLeo he wrote: "Today I submit my resignation as state representative so that I may continue to serve the people of Lawrence to the best of my ability. At this time, 'my best' means advocating from Lawrence as mayor of Lawrence."
In November 2009, Lantigua was elected mayor of Lawrence and began his term in January 2010. At the same time, he continued to hold office as a state representative. Lantigua rejected calls from fellow legislators and Governor Deval Patrick to resign one of his seats. Those demands increased in early February when Lantigua sponsored a bill allowing Lawrence to borrow $35 million from the state to bail out the city. Other representatives reportedly said the controversy jeopardized the release of funds.