Maine Mariners

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, Spectra's parent company and 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. On November 29, the Mariners' logo and color scheme were revealed. On February 17, 2018, the Mariners hired Riley Armstrong as head coach and Keith Rosenberg as on-ice assistant coach. On April 9, 2018, the Mariners announced they would be affiliated with the NHL's New York Rangers.

The new Mariners played their first game on October 13, 2018, a 6–3 loss to the Adirondack Thunder. Their inaugural game was at home with a reported attendance of 5,291.

Due to the COVID-19 pandemic, the Mariners voluntarily suspended operations for the 2020–21 ECHL season. On June 30, 2021, the Mariners entered an affiliation agreement with the NHL's Boston Bruins and their AHL affiliate, the Providence Bruins, beginning with the 2021–22 season. The Bruins were the affiliate of the original AHL Mariners from 1987 to 1992 when they relocated the Mariners' franchise to Providence. In August 2021, head coach Armstrong was hired by the Philadelphia Flyers as an assistant coach with the Lehigh Valley Phantoms in the AHL and was replaced by the University of Maine men's hockey assistant coach and former NHL player Ben Guite.

On April 16, 2022, the Mariners clinched their first-ever playoff berth thanks to the Worcester Railers dropping their game to the Trois-Rivières Lions in OT and the Mariners beating the Newfoundland Growlers, clinching the final (4th) playoff spot in the North Division.

In their first playoff series in team history, the Mariners lost to the Reading Royals, losing the series 4-2. The Maine Mariners were able to clinch a playoff spot again in the 2022-23 ECHL season, getting the #3 seed in the division. They again played the Reading Royals in the first round and lost the series 4-2.