There are just 6 players in the history of MLB who have had 500 at bats in their only season in the big leagues. The two most recent players played one year apart. Art Mahan was a 1B for the 1940 Philadelphia Phillies. He played in 146 games, had 544 ABs, 133 hits and hit .244, 2, 39. He also pitched in a game, throwing a scoreless inning, giving up 1 hit. According to baseball reference, there was no reason given for why Mahan played just the one season. A year later, Johnny Sturm; perhaps a longtime Yankees fan may remember Johnny Sturm, spent his one MLB season as the New York 1B for the 1941 season. Sturm played in 124 games, batted 524 times, hitting .239, 3, 36. He also went 6-21 (.286) in the 5 games of the 1941 World Series against the Dodgers, driving in 2 runs in the Yankees win. Sturm served the country in World War II without playing after 1941 before enlisting. He lost a finger in the war and was unable to make a full comeback in spite of playing minor league ball in 1946 and 1947.
The similar feat, but more broad statistic is those players who played in 120+ games in their only season in the big leagues. A teammate of Mahan in Philadelphia, Ham Schulte, was the starting second baseman on the 1940 Phillies team. Schulte played in 120 games, batted 436 times, and hit .236, 1, 21. In addition, he led all NL 2B in fielding percentage. After the 1940 season, he was sold to the Hollywood Stars of the Pacific Coast League and never returned to the big leagues. As well as Sturm, he served the country in WWII from 1943-1945.
Sturm was credited as one of the scouts who discovered Mickey Mantle. I find it hard to imagine a player good enough to be a starter for a MLB team, but only play one full season and have it be it. Incredible.