John Curtis, a left-handed pitcher, embarked on his Major League Baseball career with the St. Louis Cardinals. Drafted in the first round of the 1968 MLB Draft, Curtis made his debut with the Cardinals in 1970. His early years with the team were marked by a learning curve typical of young pitchers adjusting to the major leagues. During his time with the Cardinals, Curtis honed his skills and developed a reputation for his control and poise on the mound.

In 1973, Curtis was traded to the Boston Red Sox, where he spent the next few seasons. His tenure with the Red Sox saw him become a regular part of the starting rotation. Curtis's performance during this period was characterized by steady improvement, as he gained more experience and confidence. He played a crucial role in the Red Sox's pitching staff, providing reliable innings and contributing to the team's competitive efforts in the American League.

Curtis's journey continued as he joined the St. Louis Cardinals again briefly before moving to the San Francisco Giants in 1976. With the Giants, Curtis found a new home and continued to pitch effectively. His time in San Francisco was marked by consistent performances, and he became a dependable starter for the team. Curtis's ability to adapt to different teams and maintain his performance level was a testament to his skill and understanding of the game.

In 1979, Curtis signed with the San Diego Padres, where he continued to showcase his pitching abilities. His experience and veteran presence were valuable assets to the Padres' pitching staff. Curtis's career with the Padres was marked by his ability to deliver solid outings and mentor younger pitchers on the team.

The final chapter of Curtis's MLB career came with the California Angels, where he played until 1984. During his time with the Angels, Curtis transitioned into a role that included both starting and relieving, demonstrating his adaptability and willingness to contribute in various capacities. His career with the Angels allowed him to extend his time in the majors and continue to compete at a high level.

Throughout his career, John Curtis was known for his control and consistency on the mound. He pitched in over 400 games, accumulating a respectable number of wins and strikeouts.