Career
Before playing in the NHL, Määttä played two seasons with the London Knights of the Ontario Hockey League (OHL). He had a successful time with London. He helped the Knights during the playoffs. They defeated the Windsor Spitfires, Saginaw Spirit, and Kitchener Rangers before defeating the Niagara IceDogs four games to one to win the J. Ross Robertson Cup. This earned them a spot in the Memorial Cup tournament. The Knights were eventually defeated by the Shawinigan Cataractes 5-1 in overtime in the final game.
He was drafted 22nd overall by the Pittsburgh Penguins in the 2012 NHL entry draft. On 12 September 2012, Määttä signed a three-year, $2.775 million entry-level contract to join the Penguins. He was sent down to play for their AHL-affiliate Wilkes-Barre/Scranton Penguins.
On 3 October 2013, Pittsburgh called him up and Määttä made his NHL debut in a 3–0 win against the New Jersey Devils. On 8 October, he recorded his first two NHL points after assisting on two goals from Jussi Jokinen in a 5–2 win against the Carolina Hurricanes. On 19 October, Määttä scored his first NHL goal on the powerplay against Roberto Luongo in a 4–3 shootout win against the Vancouver Canucks. On 27 October 2014, Määttä was forced to take some time off and have surgery done to remove a tumour from his neck which was possibly a low-grade thyroid cancer. He had to miss 3–4 weeks after suffering an upper-body injury when he was boarded by Minnesota Wild player Nino Niederreiter on 18 November 2015. On 26 February 2016, Määttä signed a six-year, $24.5 million contract to stay with the Penguins. He helped the Penguins during the playoffs. They defeated the New York Rangers, Washington Capitals, and Tampa Bay Lightning. They went on to defeat the San Jose Sharks four games to two in the Final to win the Stanley Cup. Määttä and the Penguins made it back to the Stanley Cup Final the next year where they won their second Stanley Cup in a row.
On 15 June 2019, the Penguins traded Määttä to the Chicago Blackhawks in exchange for Dominik Kahun and a 2019 fifth-round draft pick. He scored 4 goals and recorded 13 assists for 27 points in 65 regular season with the games. He also scored 3 goals and recorded 3 assists in 9 playoff games.
On 4 October 2020, the Blackhawks traded Määttä to the Los Angeles Kings in exchange for Brad Morrison. He played two seasons with the Kings.
On 13 July 2022, Määttä signed a one-year, $2.25 million contract to join the Detroit Red Wings. On 16 February 2023, Määttä signed a two-year, $6 million contract to stay with the Wings.
On 30 October 2024, the Red Wings traded Määttä to the Utah Hockey Club in exchange for a 2025 third-round draft pick. The team later changed its name to the Utah Mammoth. He scored 2 goals and recorded 17 assists over two seasons with Utah.
On 4 March 2026, the Mammoth traded Määttä along with Jonathan Castagna and three second-round draft picks to the Calgary Flames in exchange for MacKenzie Weegar. He scored 2 goals and recorded 12 assists in 21 regular season games with the Flames.
On 2 July 2026, the Flames traded Määttä along with Blake Coleman to the Minnesota Wild in exchange for Jake Middleton, a 2029 second-round draft pick, a 2027 third-round draft pick, and a 2028 fourth-round draft pick..
Finland