In 1967, the two-time All-American was drafted No. two overall by the Baltimore Bullets (now the Washington Wizards) in the first round of the 1967 NBA draft, behind Jimmy Walker, who was selected by the Detroit Pistons. Monroe then won the NBA Rookie of the Year Award in a season in which he averaged 24.3 points per game. He scored 56 points in a game against the Los Angeles Lakers, the third-highest rookie total in NBA history. It was also a franchise record, later broken by Gilbert Arenas on December 17, 2006.
Monroe and teammate, future Naismith Basketball Hall of Fame inductee Wes Unseld, quickly became a formidable combination in Baltimore, and Monroe became a cult hero for his ability to run the fast break and for his circus-like shots. He said, "The thing is, I don't know what I'm going to do with the ball, and if I don't know, I'm quite sure the guy guarding me doesn't know either." 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. However, the Bullets were swept by the New York Knicks 4–0 in the playoffs after receiving a bye.
The Bullets finished 50–32 in 1969–1970, as Monroe averaged 23.4 points, 4.9 assists and 3.1 rebounds, making the NBA All-Star team. The Bullets were again beaten by the Knicks 4–3 in the playoffs.
In 1970–1971, the Bullets finished 42–40 under Coach Shue and captured the Central Division title. Monroe averaged 21.4 points, 4.4 assists and 2.6 rebounds. In the Eastern Conference playoffs, the Bullets defeated the Philadelphia 76ers 4–3, and then defeated the Knicks 4–3 in the Eastern Conference Finals to reach the 1971. NBA Finals. Monroe averaged 23.0 points, 4.0 assists and 3.4 rebounds in the Philadelphia series. He then averaged 24.4 points, 4.3 assists and 3.4 rebounds against the Knicks, including 26 points, 6 assists and 5 rebounds in Game 7's 93–91 Bullets victory.
In the 1971 NBA Finals, the Bullets were matched against the Milwaukee Bucks with Kareem Abdul Jabbar, Oscar Robertson and Bobby Dandridge. The Bucks swept the Bullets 4–0. Monroe averaged 16.3 points, 4.0 assists and 4.0 rebounds in the series.
"Put a basketball in his hands and he does wondrous things with it," Bullets Coach Gene Shue said of Monroe. "He has the greatest combination of basketball ability and showmanship."
In 328 games with the Bullets, Monroe averaged 23.7 points, 4.6 assists and 3.7 rebounds.
