John Peter Thielman (May 20, 1879 – January 28, 1928) was a German-American pitcher in Major League Baseball who played from 1905 through 1908 for the St. Louis Cardinals (1905–1906), Cleveland Naps (1907–1908) and Boston Red Sox (1908). Listed at 5 ft 11 in (1.80 m), 175 pounds (79 kg), Thielman batted and threw right-handed. He was born in St. Cloud, Minnesota. His younger brother, Henry Thielman, also pitched in the majors.
In a four-season career, Thielman posted a 30–28 record with 158 strikeouts and a 3.16 ERA in 65 appearances, including 56 starts, 56 complete games, three shutouts, and 475⅓ innings of work.
Thielman died at the age of 48 in Minneapolis, Minnesota.