Amateur St. Amour played
junior hockey with the Laval-Laurentides-Lanaudiere Regents of the Quebec Midget AAA Hockey League. In his final season of junior hockey in 1986–87, he was considered the top prospect in the league and expected to be drafted first in the
Quebec Major Junior Hockey League (QMJHL)'s amateur draft. He won the league's scoring title that year. He was selected first overall in the QMJHL's draft in May 1987 by the league's last place team, the
Verdun Junior Canadiens ahead of
Martin Gélinas, who was selected second by the
Hull Olympiques and
François Leroux by the
Saint-Jean Castors with the third overall pick. In June, he was invited to
Canada's under-18 tryout camp, but was cut from the team early, reportedly due to his attitude. In his first season of
major junior hockey in
1987–88, St. Amour scored 20
goals, 50
assists for 70
points in 61 games as Verdun failed to move out of last place in the league. In his second season with Verdun in
1988–89, St. Amour suffered a torn
ligaments in his left shoulder and a displaced
collarbone in a game against the Saint-Jean Castors on October 30, 1988. He returned to the lineup two weeks later against the Castors on November 16, but re-aggravated the injury in the game and left after the first period. The shoulder injury would bother him for the rest of the year. At the QMJHL's Christmas break in December, St. Amour was among the players singled out by Verdun's
general manager Jacques Lemaire as having disappointed during the season and stated that changes to the roster would come in the new year. On January 8, 1989, St. Amour was traded to the
Trois-Rivières Draveurs in exchange for
Éric Charron and a sixth-round draft pick in the QMJHL draft. He appeared in 28 games, scoring 19 goals and 36 points, with Verdun before the trade. In Trois-Rivières, he added another eight goals and 29 points in 21 games. with St. Amour adding one goal and three points in four games. As a result of his excellent play, he was named the
Canadian Hockey League (CHL)'s player of the month for December, the first player from outside to the
Western Hockey League (WHL) to win the award that season. In January 1990, he was selected to play with the QMJHL All-Stars in the annual All-Star Challenge alongside teammate Larouche. He ended the regular season with 57 goals and 136 points in 60 regular season games, finishing fourth in league scoring. The Draveurs finished in second place in the league and qualified for the 1990 QMJHL playoffs, facing the
Saint-Hyacinthe Laser in the opening round. The Draveurs were upset again in the first round, losing in seven games to the Laser. In the series, St. Amour scored seven goals and 16 points.
Professional In his first year of eligibility for the
National Hockey League's (NHL)
entry draft, St. Amour was rated among those who could go in the second round. Gélinas and Leroux, who were selected behind him in the QMJHL draft, were considered better prospects for the NHL. St. Amour was selected in the second round, 34th overall, in the
1988 NHL entry draft by the
Montreal Canadiens. The second-round pick was acquired by Montreal in a trade with the
Buffalo Sabres for defenceman
Tom Kurvers. He attended Montreal's training camp in September 1989 but was returned to his junior team before the season began. After his team was eliminated from the playoffs in April 1990, St. Amour was recalled to Montreal's
American Hockey League (AHL) affiliate, the
Sherbrooke Canadiens, which were in the midst of their quarterfinal series against the
Halifax Citadels in the
1990 Calder Cup playoffs. St. Amour made one playoff appearance with Sherbrooke, going scoreless. before being assigned to their new AHL affiliate, the
Fredericton Canadiens to begin the season. In his rookie season in the AHL, St. Amour scored 13 goals and 29 points in 45 games with Fredericton, Fredericton qualified for the
1991 Calder Cup playoffs, but St. Amour only managed to appear in one game, going scoreless. However, a number of new players were brought to Fredericton by Montreal and St. Amour found himself among the players needing a new team. Fredericton's coach,
Paulin Bordeleau, publicly called out his desire to be a better hockey player while Fredericton's general manager, Jacques Lemaire, was searching for a landing place for St. Amour. Ultimately, St. Amour accepted a buyout of his contract by Montreal in October and became a free agent. St. Amour joined the
Cincinnati Cyclones of the
ECHL in October for the remainder of the
1991–92 season. Normally a
left winger, St. Amour
centered the second line, grouped with Shaun Clouston and Bobby Wallwork. St. Amour finished the season as the team's leading scorer, recording 44 goals and 88 points in 60 games with Cincinnati. The Cyclones qualified for the
1992 Riley Cup playoffs and faced the
Dayton Bombers in the first round in a best-of-five series. The Cyclones eliminated the Chiefs to advance to the West Division final against the
Louisville IceHawks. However, they fell to the IceHawks in their best-of-five series 3 games to 1. St. Amour finished second in team scoring during the playoffs, recording four goals and 13 points in nine games. In the offseason St. Amour signed a contract with the expansion
Ottawa Senators of the NHL in August 1992. He attended Ottawa's training camp but was among the players assigned to the team's AHL affiliate, the
New Haven Senators, on September 27 for the
1992–93 season. In April 1993, St. Amour was recalled by Ottawa on an emergency basis alongside
Tony Cimellaro after injuries to forwards
Darcy Loewen and
Jody Hull. He made his NHL debut on April 4, 1993 against the
Vancouver Canucks. In the second period, he was involved an altercation with the Canucks, taking a
minor penalty for
roughing alongside teammate
Sylvain Turgeon, which was offset by roughing penalties to the Canucks'
Gerald Diduck and
Petr Nedvěd. The Senators lost the game 3–0. On April 7, St. Amour was returned to New Haven. He finished the season with New Haven, recording 21 goals and 60 points in 71 games, leading the team in scoring. St. Amour was one of the players Ottawa left unprotected in the offseason, ahead of the
1993 NHL expansion draft. He was not selected, and in September he attended Ottawa's training camp. However, he was among the players assigned to their new AHL affiliate, the
Prince Edward Island Senators in the first wave of cuts. He struggled offensively with the AHL Senators in the
1993–94 season, going a month without scoring a goal. However, after falling out of favour with his coach
Don MacAdam, who openly criticized his players' commitment to play in late January 1994, St. Amour requested a trade. In 12 games with Providence, he recorded three assists. He remained with Whitley until October when he was released and replaced by Brian Verbeek. He then briefly joined the
Teesside Bombers, but was released before playing a game for them, after the team lacked the funds to pay him. In 1995 he returned to North America and played in the semi-professional leagues with the Moncton Labatt Ice of the Nova Scotia Senior Hockey League (NSSHL) beginning in February. However, the team was suspended by both the NSSHL and the New Brunswick Amateur Hockey Association after a payment for the transfer of St. Amour failed to clear and would not reinstate the team until proper funds were provided. In the 1995 offseason he joined the
San Diego Gulls of the
West Coast Hockey League (WCHL) for their inaugural season in
1995–96. Frustrated with playing in the WCHL, he claimed he would likely retire if he did not get promoted to the
International Hockey League (IHL) before the end of the season. In January 1996, he received a five-game tryout with the IHL's
San Francisco Spiders, joining the team for a four-game road trip. He played in four games with San Francisco, recording two assists. He was offered a contract by San Francisco but turned it down as the terms did not meet his requirements. He returned to San Diego on January 25. On March 21, he signed a contract of the
Long Beach Ice Dogs of the IHL and appeared in one game for them before returning to San Diego. The Gulls went on to finish top of the league in the regular season and St. Amour lead the league in goals and points. He finished the regular season with 61 goals and 109 points in 51 games. As the top team, the Gulls qualified for the playoffs and advanced to the final and won the
Taylor Cup for the first time, defeating the
Fresno Falcons. St. Amour six goals and 13 points in nine playoff games and finished as the playoff scoring leader. He returned to the Gulls for the
1996–97 season and was named
captain. Playing alongside his brother Stephane, he led the league in scoring again, recording 60 goals and 127 points in 59 games. He was once again named a first-team all-star and named the league's most valuable player. The Gulls finished first in the league and advanced to the Taylor Cup finals where they beat the
Anchorage Aces to win back-to-back championships. He signed a two-year contract with the Gulls in September 1997. In the
1997–98 season the Gulls advanced to the Taylor Cup finals versus the
Tacoma Sabercats, which they won for the third consecutive time. St. Amour recorded 35 goals and 79 points in 61 games in the regular season and 11 goals and 18 points in 12 playoff games. In the
1999–2000 season, St. Amour's playing time fell as he took over as head coach of the team after Steve Martinson was suspended, and then aggravated an injury near his
pelvic bone that had been bothering him all season. He finished the season with six goals and 16 points in 23 games. He remained with the Gulls for the
2000–01 season, but suffered injuries that limited him to 14 games, in which he scored one goal and five points. He once again took over head coaching duties after the suspension of coach Martinson. However, on January 5, 2001, ahead of a game against the Tacoma Sabercats, St. Amour announced his retirement due to injuries. At the time of his retirement, he was the franchise's leading scorer. In the midst of the
2001–02 season, St. Amour came out of retirement to play for the Gulls on a short-term basis, donning the number 81 as his original number had been retired, due to injuries within the team. He appeared in 20 games, scoring two goals and ten points. He appeared in three games, registering two assists. In 2003–04, he made a single appearance in the
Central Hockey League for the
Arizona Sundogs, going scoreless. ==Coaching career==