The team posted a Mario-inspired video on its Twitter account celebrating the news.
"Emotional. It was a process, a learning process this summer. Learning the whole business side of negotiations,'' Seguin said. "At the end of the day, I knew where I wanted to be. I knew where home was. That was here in Dallas.''
Forward Jamie Benn had been the highest-paid player on the team, with an average annual value of $9.5 million from the deal that he signed in 2016. Seguin is entering the final season of a six-year deal that will pay him $5.75 million in 2018-19.
The 26-year-old had a career-high 40 goals to go with 38 assists last season. The five-time All-Star has finished in the top 10 in goals four times in his career.
Only Benn, a two-time All-Star who is 29, had more points last season with 79 (36 goals, 43 assists) -- and that was after Benn had eight goals and two assists in his last five games.
"With Jamie Benn and Tyler Seguin, I think our franchise is in a good spot over the next eight or nine years,'' general manager Jim Nill said.
"Tyler's really coming into his prime right now. I think last year we saw him take a major step. He became one of our leaders,'' the GM said. "He's really hit the prime of his career.''
Even though the Stars have been hit-and-miss as a playoff team in Seguin's five seasons, Nill had no doubt he wanted captain Benn's prolific partner as part of a core that's locked up for several years. Alexander Radulov and defenseman John Klingberg are included in that mix.
"You don't find these guys on the Kmart shelf,'' Nill said. "He's an elite player. He's a center ice man. He's got a great skill set. And he's been an elite scorer for a long time.''
Seguin was the second overall pick in the 2010 draft by the Bruins and won a Stanley Cup with Boston in 2011. He was traded to Dallas in 2013.
Coming into the season with fairly high expectations last year, the Stars stumbled to a sixth-place finish in the Central Division, missing the playoffs for the second straight season. Coach Ken Hitchcock retired in April and Jim Montgomery was named to replace him.
The Associated Press contributed to this report.