LaPorte began riding in the early 1970s during a period of rapid growth in American motocross. He turned professional at the age of 16 and by 1976 had been offered a place on the Suzuki factory racing team. One person who was not surprised by LaPorte's eventual world championship was Roger DeCoster, who had taken LaPorte under his wing when both rode for Suzuki. Race observers noted that LaPorte's riding style bore similarities to DeCoster's, and that he possessed world-class potential.
In 1979 LaPorte won the AMA 500cc national championship for Suzuki. Injuries hampered his 1980 and 1981 seasons. He was part of the United States team that won the Motocross des Nations in 1981, marking the first time an American team had won the prestigious event.
Seeking new challenges, LaPorte sought a ride for the 1982 250cc Motocross World Championship. Most factory teams passed on his inquiries, citing his injury-interrupted recent record. At the last minute Yamaha Motors N.V. — the Dutch Yamaha importer — took a chance and placed LaPorte, then 25, on a factory bike managed by former world champion Heikki Mikkola.
LaPorte adapted well to European racing life, leasing a home in a comfortable neighbourhood of Brussels, Belgium, where he lived throughout the season with his French girlfriend. European television coverage of the races was extensive, and his Belgian neighbours would gather outside his home to welcome him back after strong results.
Reigning champion Georges Jobé on Suzuki was heavily favoured and led the championship comfortably at mid-season when he suffered an elbow fracture during the 250cc French Grand Prix. LaPorte responded by winning three consecutive Grand Prix races to take the championship points lead.
LaPorte failed to score in only two of 24 motos across the season. His results showed exceptional consistency: 6-1 in Czechoslovakia, 5-2 in Italy, 2-1 in England, 1-1 in Holland, and 1-2 in Russia. His sole appearance in the United States in 1982 was the US Grand Prix at Unadilla, New York — a hilly natural terrain circuit that draws approximately 20,000 spectators. LaPorte's 4-2 moto finishes gave him third overall on the day but padded his points lead over Jobé, who finished fifth. The first moto between LaPorte and Jobé was an intense wheel-to-wheel duel that transfixed the Unadilla crowd. Fans grabbed at LaPorte as he returned to the pits; only the snow fence kept him from being mobbed.
The championship was not settled until the final round in Sweden, where LaPorte recorded 4-2 moto finishes to claim the title by 13 points. He was the first American to take the 250cc world title.
Jobé returned for 1983 with a commanding response, winning five of the first six heat races to build a 60-point lead before clinching the title with two rounds remaining.
After returning to the United States, LaPorte switched to desert racing and won the Baja 1000 three times as a member of the Kawasaki racing team. In the 1990s he expanded into international rally raids, winning the 1991 Pharaohs Rally in Egypt. In 1992 he finished second overall in the Paris-Dakar Rally, also winning a stage.
LaPorte was inducted into the AMA Motorcycle Hall of Fame in 2000 and again in 2003 as a member of the victorious 1981 Motocross des Nations team. He has also been inducted into the Motorsports Hall of Fame of America. He resides in Southern California.