Sampson played college soccer at San Jose State University and was an assistant at UCLA from 1982 to 1985. His first major head coaching job was at Santa Clara University, whom he led to the NCAA co-championship in 1989. Sampson became an assistant to Bora Milutinovic on the United States national team in 1993 and was on the staff when the U.S. hosted the 1994 World Cup. As Bora resigned from the team, Sampson became the interim coach in April of 1995. But after leading the US to a surprising fourth-place finish that included a 3-0 romp over Argentina in the 1995 Copa Am�rica, he was promoted to being the full-time coach in August of that year.

Unfortunately for Sampson, it was in his first year that he peaked as U.S. coach. The U.S. lost only one match in qualifying for the 1998 World Cup, but it was all downhill from there. Sampson dismissed long-time captain John Harkes from the team, and switched to a 3-6-1 formation just before the tournament, using inexperienced Chad Deering and Brian Maisonneuve as his defensive midfielders. The US flopped in the World Cup, losing all three of its games, and Sampson was promptly fired.

Sampson re-surfaced on the international scene as the head coach of the Costa Rica national team in 2002. He did not survive the qualifying campaign for the 2006 World Cup, and was fired in 2004 after Costa Rica needed away goals to get past unfancied Cuba. He was hired as the Galaxy coach, replacing Sigi Schmid, on August 18, 2004. After the team flopped the rest of the year and struggled for large stretches of 2005, the Galaxy turned it on late, and won the U.S. Open Cup and MLS Cup double, the last as the lowest seed in the playoffs. Sampson was relieved of his duties as Galaxy coach on June 6, 2006. The Galaxy were in last place with a record of 2 wins, 8 losses, 1 draw at the time of Sampson's firing.