State Representative Dan Cullinane said Wednesday he will not run for reelection this fall, opening up a seat that represents diverse swaths of Dorchester, Mattapan, and Milton.

In a statement, the Democrat said that “taking a step back from the demands of public life at the conclusion of this term is the right decision for my young family,’’ but added that the choice to recede from political life was “the hardest decision of my professional career.’’

Cullinane was first elected to the House in a 2013 special election to fill the seat left vacant when Linda Forry won election to the Senate. He topped a three-candidate field in that special election and has had competition from other Democrats in each of his three subsequent reelection campaigns. Cullinane said he and his wife have added two children to their family in recent years and said now is “the right time to move on from elected office to put my family first.’’

Before his election to the House, Cullinane worked on Forry’s Senate campaign and held positions on the staffs of then-Representative Martin Walsh and then-City Councilor Maureen Feeney.

This session, Cullinane served as House vice chair of the Committee on Health Care Financing. That committee is currently without a chairperson, since Speaker Robert DeLeo has not yet filled the position following Representative Jennifer Benson’s resignation to run the Alliance for Business Leadership.