Having an all-star defenseman for a brother convinced the younger Pronovost that playing a well-rounded brand of hockey with defense as a foundation was the best way to insure success. The first fruits came while skating for the Niagara Falls Flyers where, in his first season with the club, they beat the Edmonton Oil Kings to take the Memorial Cup in 1965. Pronovost remained with the club for an additional year before joining the Boston Bruins' affiliate in Oklahoma City. There, the winning trend continued as the Blazers won the Adams Cup as champions of the CHL.

In 1968, however, the Bruins committed a serious error when they sold Pronovost to the Pittsburgh Penguins. With the Pens, his full potential came to the surface. Over the next ten seasons, he was a pillar of consistency, cruising his lane with speed and determination, defending against foes, digging into corners, making smart passes, and picking up the big goals.

In 1975-76, on a line with Syl Apps, Jr. and Lowell McDonald, he achieved the pinnacle of his career when he scored 52 goals in 80 games. In 1978, Pronovost was traded to the Atlanta Flames for Gregg Sheppard. In Georgia, Pronovost continued to play his usual rock-solid, two-way game. But the club failed to generate even a hint of contending for the Cup?the one elusive achievement lacking in his career. He noted that the Flames had talent, but they appeared, from his perspective, to lack the necessary desire to win.

Pronovost's final two NHL seasons were spent with the Washington Capitals where, unlike Atlanta, the club had loads of desire but not enough talent to travel up the standings. As such, he toiled for a season and a half, jumped down to the AHL's Hershey Bears for 69 games and then retired from hockey.