Amateur Välimäki was selected 14th overall by the
Tri-City Americans of the
Western Hockey League (WHL) in the 2015
Canadian Hockey League Import draft. He debuted with the Americans in the
2015–16 season, playing in 56 games, scoring seven
goals, 25
assists for 32
points. He returned to Tri-City for the
2016–17 season, improving his scoring, recording 19 goals and 61 points in 60 games. The Americans made the 2017 WHL playoffs and faced the
Seattle Thunderbirds in the first round best-of-seven series. Tri-City was swept in four games, with Välimäki recording just one assist in the series. In his third and final season with Tri-City, he appeared in just 43 games, marking 14 goals and 45 points. The Americans made the 2018 WHL playoffs and swept their first round series with the
Kelowna Rockets and their second round series against the
Victoria Royals. However, in the third round, they ran into their division rival, the
Everett Silvertips, and were eliminated in six games. In the Americans' 12 playoff games, Välimäki added four goals and 17 points and was a "rock on the blueline". and ranked the 14th skater by
ISS Hockey. He was selected by the
Calgary Flames in the first round, 16th overall, before signing a three-year, entry-level contract with the Flames on 21 July 2017. Välimäki opened the
2018–19 season with the Flames after making the team out of training camp. He made his NHL debut on 3 October 2018, against the
Vancouver Canucks. He scored his first NHL goal on 17 October, the third Flames goal in a 5–2 victory over the
Boston Bruins; Välimäki scored the goal on
Tuukka Rask, who had lost control of the puck after initially catching a piece of Välimäki's shot. Välimäki suffered a
high ankle sprain on 23 November in a game against the
Vegas Golden Knights which limited his season. He was assigned to Calgary's
American Hockey League (AHL) affiliate, the
Stockton Heat, on 22 January 2019 and played in 20 AHL games, registering four goals and 14 points. The Flames were eliminated by the Avalanche in five games, and Välimäki recorded the one assist in the two games he played in the series. While training in the offseason, Välimäki suffered a torn
ACL injury that required surgery to repair. Though he was healthy when play resumed in August 2020 for the
2020 Stanley Cup playoffs, Calgary had replaced him in the lineup with trade acquisitions and Välimäki was a healthy scratch. As the following North American season was delayed due to the pandemic, Välimäki was loaned by the Flames to Finnish
Liiga club,
Ilves, to start the
2020–21 season on 30 September 2020. Välimäki made a successful return from injury with Ilves, playing in a key role and producing at a point-per-game pace through 19 regular season contests, recording two goals and 17 assists. He began the
2021–22 season with the Flames, though was rarely utilised, appearing only eight times in the first two months and was a healthy scratch 15 times. He was assigned to Stockton on 2 December. and appeared in one more game. In total he made nine appearances for Calgary, recording two assists.
Arizona Coyotes Prior to the
2022–23 season, after being unable to make the Flames opening night roster, Välimäki was placed on
waivers before he was claimed the following day, on 9 October 2022, by the
Arizona Coyotes. He made his Coyotes debut on 17 October in a 4–2 win over the
Toronto Maple Leafs. He recorded his first point with the Coyotes on two games later on 22 October, assisting on
Dylan Guenther's first career NHL goal in the second period of a 6–2 loss to the
Ottawa Senators. He scored his first goal in a Coyotes uniform on 3 November in the third period to break
Scott Wedgewood's shutout bid in a 7–2 loss to the
Dallas Stars. On 11 February 2023, he recorded four assists in a 6–5 overtime loss to the
St. Louis Blues. He registered a three-point night on 18 March, scoring one goal and marking two assists in a 4–2 victory over the Chicago Blackhawks. Establishing a regular role within the Coyotes on the blueline, Välimäki was signed to a one-year, $1 million contract extension at the mid-point of the season on 24 January 2023. He finished the season with four goals and 34 points in 78 games with the Coyotes. He underwent surgery to fix the damage, but the process in which he was left for several hours without care at a
Dallas hospital was investigated by both the NHL and the
National Hockey League Players' Association. He returned to the lineup on 30 November after missing six games. In January 2024 he went through a period of healthy scratches as the depth of defencemen on the Coyotes reached its peak with everyone returning from injury. He finished the season with two goals and 17 points in 68 games. In the 2024 offseason, he signed a two-year contract with Utah on 29 June. After playing in 43 games for the Mammoth in the
2024–25 NHL season, registering two goals and five points, he was placed on waivers on 25 February and assigned to Utah's AHL affiliate, the
Tucson Roadrunners. In his first game playing for Tucson, Välimäki tore his
ACL on 28 February and was expected to be out for nine months to recover. On 28 December 2025, Välimäki was placed on waivers by the Mammoth to be assigned to the Tucson Roadrunners. He made three appearances for Tucson, scoring one goal and three points.
Carolina Hurricanes On 5 January 2026, Välimäki was traded by the Mammoth to the
Carolina Hurricanes in exchange for future considerations. ==International play==