He played in Major League Baseball as a left-handed pitcher with the Los Angeles Dodgers (1962–64, 1972–73), Washington Senators (1965–67), Baltimore Orioles (1967–71), St. Louis Cardinals (1974) and Philadelphia Phillies (1974).

[5][4] 1960 was his best minor league year, playing for the Class-AA Atlanta Crackers of the Southern Association, with a 19–9 win-loss record, 2.76 earned run average (ERA), 251 strikeouts in 225 innings, 18 complete games and six shutouts.

In his Major League debut on April 12, 1962, against the Cincinnati Reds at Dodger Stadium, Richert set a record by striking out the first six batters he faced.

Richert then recorded a four-strikeout third inning in which his victims were Frank Robinson (his future Baltimore Orioles teammate), Gordy Coleman (who reached first base on a passed ball by John Roseboro), Wally Post and Johnny Edwards; his record-tying sixth strikeout was of Tommy Harper leading off the fourth.

[1][9] After the 1964 season, Richert, Frank Howard, Ken McMullen, Dick Nen and Phil Ortega were traded to the Washington Senators for pitcher Claude Osteen, infielder John Kennedy and $100,000 cash.

[3] He was the losing pitcher in the 1966 game, giving up a single to former Dodgers teammate Maury Wills, which scored Tim McCarver for the winning run in the 10th inning.

[3][14] After going 2–6 to start the 1967 season, Richert was acquired by the Baltimore Orioles in a deal sending Mike Epstein and Frank Bertaina to Washington.

[1] The Orioles lost the World Series in surprising fashion to the New York Mets, and Richert was involved in a controversial play which ended Game 4.

In the bottom of the 10th, with the game tied at 1–1, J. C. Martin laid down a bunt and was hit by Richert's throw; the error allowed Rod Gaspar to score the winning run from second.

[1] Richert returned to the Dodgers upon being traded, along with Frank Robinson, from the Orioles for Doyle Alexander, Bob O'Brien, Sergio Robles and Royle Stillman at the Winter Meetings on December 2, 1971.

[1] After pitching in a September game, he learned he had a blood clot in his shoulder that required surgery, that ultimately involved moving a vein in his body, and necessitated his retirement.

He originally became a minor league pitching coach through the recommendation of former Orioles teammate Merv Rettenmund, and did that for 14 years, 12 with the Oakland Athletics' farm system.