He played for two teams, the Baltimore Bullets and the New York Knicks, during his career in the National Basketball Association (NBA).

Due to his on-court success and flashy style of play, Monroe was given the nicknames "Black Jesus" and "Earl the Pearl".

He worked as a shipping clerk in a factory, while frequently playing basketball at Leon Whitley's recreation center in Philadelphia.

During that 1966–1967 season, Jerry McLeese, a sportswriter for the Winston-Salem Journal, called Monroe's points "Earl's pearls".

The 40-person committee failed to select both Monroe and fellow future Hall of Fame player Elvin Hayes.

[12][7][13][14] Monroe has said that USA coaches said his style of play was "too street, too playground, too black" adding, "It has always left a very, very bad taste in my mouth.

He scored 56 points in a game against the Los Angeles Lakers, the third-highest rookie total in NBA history.

"[15] On February 6, 1970, he set an NBA record with 13 points in one overtime in a double-overtime victory over the Detroit Pistons (another mark since surpassed by Arenas).

In 1968–1969, Monroe averaged 25.8 points, 4.5 assists and 3.9 rebounds, as the Bullets finished 57–25 under coach Gene Shue, capturing the Eastern Division title.

Oscar Robertson, Walt "Clyde" Frazier, Tom Van Arsdale, Hal Greer, and Flynn Robinson were the guards selected.

[20][21] In the 1971 NBA Finals, the Bullets were matched against the Milwaukee Bucks with Kareem Abdul-Jabbar, Oscar Robertson and Bobby Dandridge.

After four games into the 1971–1972 season, he traveled to Indianapolis to discuss a transfer to the American Basketball Association's Indiana Pacers.

He eventually signed a contract immediately after being sent from the Bullets to the New York Knicks for Mike Riordan, Dave Stallworth and an undisclosed amount of cash twenty days later on November 11, 1971.

While there were initial questions as to whether Monroe and Frazier could coexist as teammates, the duo eventually meshed to become one of the most effective guard combinations of all time.

[27] In the 1972 NBA Finals, the Knicks were defeated by the Los Angeles Lakers with Jerry West and Wilt Chamberlain 4–1, losing four straight after winning Game 1.

A four-time NBA All-Star, Monroe retired after the 1980 season due to serious knee injuries, which had plagued him throughout his career.

[10] Overall, Monroe played in 926 regular season NBA games, scoring 17,454 total points with 3,594 assists on 46% shooting.