On May 23, 2016, the Portland Pirates' franchise was sold and relocated to Springfield, Massachusetts, and became the Springfield Thunderbirds. A team of investors headed by former Pirates executives W. Godfrey Wood and Brad Church—the latter a former Portland player as well—announced their intentions to put an ECHL team in Portland to fill the void, joining as early as 2017. However, progress to attain a franchise by the Portland group stalled until four groups, none of which involved Wood, submitted their own proposals at the end of February 2017. By March 8, the arena owners had narrowed their choices to the proposals submitted by Spectra and National Sports Services, with both groups having been involved with managing ECHL teams in their past.
In June 2017, Comcast Spectacor, the operators of the Cross Insurance Arena and the NHL's Philadelphia Flyers -- the founders and NHL affiliate for years of the original Maine Mariners AHL franchise in Portland -- purchased the franchise rights of the recently dormant Alaska Aces of the ECHL. The league approved of the sale and relocation of the franchise to Portland on June 15.Philadelphia Flyers president Paul Holmgren, will serve as the team’s governor with former player Danny Briere overseeing the day-to-day operations. In August 2017, the team announced their five finalists for a team name: the Mariners, Watchmen, Lumberjacks, Puffins, and Wild Blueberries. The name was announced as the Mariners on September 29.