Lalas rose to national prominence while playing for Rutgers University, leading them to the NCAA Championship Game in 1990. In 1991, he was named a First Team All American and also won both the Hermann Trophy and the Missouri Athletic Club Player of the Year award.
After graduating from Rutgers in 1991, Lalas did not sign with a club and played exclusively for the United States national team. Between 1991 and 1998, he earned 96 caps and scored 9 goals for the national side.
A charismatic and colorful character, with his trademark long red hair and a beard, Lalas achieved near-celebrity status during the 1994 World Cup. He started and played every minute in the US's four matches, until they were eliminated by eventual winners Brazil in the first knockout round.
Lalas' performance in the World Cup drew the attention of Padova, who had just been promoted to Serie A for the 1994-95 season. Padova finished at the bottom of the table in 1995, but won a relegation playoff to remain in the top flight. At the end of that season, Lalas signed a contract with MLS to play in the new league's inaugural season, but MLS had to delay its start until 1996, so it loaned Lalas back to Padova for the 1995-96 season.
In 1996, Lalas signed for the New England Revolution, where he played until December 1997 (including a brief period on loan with Ecuadorian side Emelec). He spent the next several years with various MLS clubs, including the NY/NJ Metrostars, Kansas City Wizards, and Los Angeles Galaxy.
After his playing career ended, Lalas spent time as a broadcaster as well as serving as the general manager of the San Jose Earthquakes, Metrostars/Red Bulls, and the Galaxy.