In an eight-season career, Blefary was a .237 hitter with 112 home runs and 382 RBI in 974 games.

In his debut year of 1965, Blefary hit .260 with 22 home runs and 70 RBI, winning both the American League Rookie of the Year and The Sporting News Rookie of the Year awards. The following season, he was a member of the Orioles team that won the 1966 World Series.

Nicknamed "Clank" by Frank Robinson, in part for his below-average fielding abilities, Blefary started his career in the outfield, tried at first base, then switched to catcher, in an effort to keeping his bat in the lineup. On April 27, 1968, he caught Tom Phoebus's no-hitter against the Red Sox. Blaming his constant defensive shuffling for his offensive decline, Blefary was sent to Houston in 1969 in the deal that brought Mike Cuellar to the Orioles.

After a full-season with the Astros, Blefary was used as a part-time player by the Yankees, Athletics and Padres. After retiring in 1972, he tried unsuccessfully to continue his career in baseball as a coach. He worked as a sheriff, bartender, truck driver, and later owned a night club. Even as his health failed in his later years, he hoped to secure a professional coaching job, but his only connection with baseball was as a volunteer coach for Northeast High School in Fort Lauderdale.

Blefary died in Pompano Beach, Florida, at age 57. His last wish was to be buried in Baltimore's Memorial Stadium. Although the park was nearly demolished when he died, his wife Lana was able to honor his request to scatter his ashes in Memorial Stadium. The Babe Ruth Museum supplied the home plate used in the penultimate game at the stadium and located it in the precise spot where it had been used. The ceremony was held on May 24, 2001. "He loved Baltimore, and he loved his fans," said his wife. "He was a lifelong student of the game."