John Lowenstein's journey in Major League Baseball began when he was drafted by the Cleveland Indians in the 1968 amateur draft. He made his major league debut with the Indians in 1970, showcasing his skills as an outfielder and infielder. Lowenstein's early years with Cleveland were marked by his adaptability on the field, as he played multiple positions, including second base and the outfield. His versatility allowed him to fill various roles for the team, although he primarily played as an outfielder.

During his tenure with the Indians, Lowenstein developed a reputation for his left-handed batting and his ability to perform in clutch situations. Despite not being a regular starter, he contributed significantly when called upon, often coming through with key hits. His time with Cleveland lasted until 1977, when he was traded to the Texas Rangers.

Lowenstein's stint with the Rangers was brief, as he played only one season with the team. In 1978, he was traded to the Baltimore Orioles, where he would spend the remainder of his career. It was with the Orioles that Lowenstein found a more consistent role, often platooning in left field. His ability to hit right-handed pitching made him a valuable asset in the Orioles' lineup.

The 1979 season was a highlight for Lowenstein, as he played a crucial role in helping the Orioles reach the World Series. Although the team ultimately fell to the Pittsburgh Pirates, Lowenstein's performance during the season and the playoffs was commendable. He continued to be an important part of the Orioles' roster in the following years, contributing to their success in the American League.

In 1983, Lowenstein was part of the Orioles team that won the World Series, defeating the Philadelphia Phillies. His experience and steady play were instrumental in the team's championship run. Lowenstein's ability to perform under pressure and his knack for timely hitting were assets that the Orioles relied upon throughout his time with the team.

Lowenstein retired from professional baseball after the 1985 season. Over the course of his career, he played in 1,268 games, amassing 1,021 hits, 116 home runs, and 521 runs batted in. His career batting average stood at .253. Known for his sense of humor and engaging personality, Lowenstein was a popular figure in the clubhouse and among fans.

After retiring from playing, Lowenstein transitioned into broadcasting, where he continued to share his love for the game.