Major junior Amadio was a prolific scorer playing in Northern Ontario's bantam and midget levels, before he was selected by the
Brampton Battalion of the
Ontario Hockey League (OHL) in the second round, 36th overall, of the 2012 OHL Priority Selection draft. In his OHL rookie season in
2012–13 he appeared in 63 games, scoring six
goals, 13
assists and 19
points. In the offseason the Battalion were relocated to
North Bay, Ontario to become the
North Bay Battalion. In his second season with the franchise in
2013–14, Amadio tallied 12 goals and 38 points in 64 games and added another four goals and nine points in North Bay's 22 playoff games. Ahead of the
2015–16 season, Amadio was named the
captain of the Battalion. He scored a franchise record of 50 goals that season in 68 games, registering 98 points and was nominated for the
Red Tilson Trophy and
William Hanley Trophy. Amadio was named the winner of the William Hanley Trophy on April 22, 2016, and was later selected for the OHL Second All-Star Team.
Professional Los Angeles Kings Amadio was selected by the
Los Angeles Kings of the
National Hockey League (NHL) with the last pick in the third round, 90th overall, of the
2014 NHL entry draft. He was then reassigned to join their
American Hockey League (AHL) affiliate, the
Ontario Reign for their playoff run following the
2015–16 season. In 11 post-season games he contributed with one goal and five points. He made his NHL debut that night in a 4–0 shutout victory over the
Montreal Canadiens. In his fourth game, Amadio registered his first NHL goal, scoring in a 5–3 victory over the
Toronto Maple Leafs on November 2, 2017. He was returned to the Reign, going on a 17-game point streak in the AHL but was recalled in January and remained with the Kings into March. He recorded his first multi-point game on January 21, 2018, when he scored a
powerplay goal and assisted on another powerplay goal by
Tanner Pearson in a 4–2 victory over the
New York Rangers. He played in 32 regular season games with Ontario, scoring 11 goals and 35 points and in 37 games with Los Angeles, tallying four goals and eight points. He also appeared in the Reign's
2018 Calder Cup playoffs run, playing in four games, scoring one goal and four points. After playing in 28 games, Amadio was reassigned to the Ontario Reign. Despite recalls throughout the season, he was again assigned to the Ontario Reign after the Kings failed to clinch a post season berth. He made 43 appearances with the Kings, marking six goals and 13 points and added another eight goals and 26 points in 28 games with Ontario. He once again made the Kings opening night roster out of training camp in
2019–20. He played in 68 games with Los Angeles, scoring six goals and 16 points, He began the pandemic-shortened
2020–21 season with the Kings, and appeared in 20 games, registering only two assists. He was placed on
waivers on March 19 and went unclaimed. He was then assigned to the Kings'
taxi squad. He also appeared for the Reign, where he played two games, adding two assists.
Ottawa Senators and Toronto Maple Leafs On March 29, 2021, Amadio was traded to the
Ottawa Senators in exchange for defenceman
Christian Wolanin. He made his Senators debut on April 8, in a 3–1 loss to the
Edmonton Oilers. He registered his first point with Ottawa in the next game, assisting on
Tim Stützle's goal in a 6–5 loss to the Toronto Maple Leafs. He made five appearances with the Senators following the trade, registering the one assist. Amadio signed a one-year, two-way contract with the Toronto Maple Leafs on July 29, 2021. After
Ilya Mikheyev was injured during training camp, Amadio beat out
Adam Brooks for the final lineup spot on the Maple Leafs opening night roster to commence the
2021–22 season. Vegas claimed him after placing
Nolan Patrick on injured reserve and were dealing with a shortage of healthy forwards. He made his Golden Knights debut on November 2 in a 4–0 shutout loss to his former team, the Maple Leafs. He registered his first point with Vegas on December 1, assisting on
William Carrier's second period goal in a 6–5 loss to the
Anaheim Ducks. He scored his first goal for the Golden Knights in the next game, a two-point effort in a 7–1 win over the
Arizona Coyotes. On January 30, 2022, the Golden Knights signed Amadio to a two-year, $1.525 million contract extension. He marked a three-point night scoring one goal and registering two assists in a 5–4 victory over the Anaheim Ducks on March 5. He finished the season playing in 53 games with Vegas, scoring 11 goals and 18 points. He changed his game in Vegas from that of a playmaker to a more direct style and soon made earned himself a role that saw his playing time increase. He finished the season with 16 goals and 27 points in 67 games. Amadio finished the playoffs with five goals and ten points including a goal in the series-clinching game five of the
2023 Stanley Cup Final, where the Golden Knights won the
Stanley Cup. On July 19, Amadio was awarded the key to the city of Sault Ste. Marie by Mayor Matthew Shoemaker when he brought the Stanley Cup to the city. In
2023–24 Amadio was now an established regular on the Golden Knights as the team made few changes to the roster that won them the Stanley Cup. A bottom-six forward with Vegas, he played in 73 games, scoring 14 goals and 27 points. ==Career statistics==