Clark was sworn on January 5, 2011. She is a pro-choice legislator and has been endorsed in her campaigns by both NARAL Pro-Choice Massachusetts and the Planned Parenthood Advocacy Fund.
In 2011, she was co-chair of the Joint Committee on Public Service, where she was lead author of the Senate version of a bill to reform municipal pensions. For her work in 2011, she received legislator of the year awards from the Massachusetts Municipal Association and the Massachusetts Police Association. In 2012, she authored a law that takes steps to ensure that all Massachusetts students are reading at grade level by third grade. Also in 2012, her bill extending restraining orders in domestic violence cases to also cover victims' pets, which are often used as pawns in abusive relationships, was signed as part of a larger law on animal shelters. In 2013, she co-sponsored a bill expanding the state's wiretapping authority, which was strictly limited under existing law, in order to help police better investigate violent street crime. At the same time, she co-sponsored a bill to secure electronic privacy protections, requiring police to have probable cause before investigating the electronic records of individuals. She filed another bill tightening sex offender laws, imposing stricter penalties and making offender data more accessible to agencies and the public. The Women's Bar Association of Massachusetts honored Clark as their 2013 Legislator of the Year for her service on women's issues.