Sevcik was a catcher and was listed at 6 feet 2 inches (1.88 m) tall and 205 pounds (93 kg) and threw and batted right-handed.

John was born on July 11, 1942 in Oak Park, Illinois, to Joseph and Helen Sevcik (née Urban), twenty minutes after his twin brother James (known as "Jim").

[3] As he had signed under the bonus rule then in force, Sevcik spent the entire 1965 season on the roster of the Minnesota Twins.

He appeared in 12 games that season, with one hit (a double off Wally Bunker of the Baltimore Orioles September 28) in 16 at bats (.063) and one run scored.

[6] After his baseball career ended, the couple initially lived in Minneapolis, Minnesota where Glenda opened an interior design and antiques business and John worked in construction equipment sales.