Barney Dreyfuss, owner of the Pittsburgh Pirates, invited Lobert to try out for his team in September 1903. He started his professional baseball career at the age of 21 that same month. Like shortstop Honus Wagner, a teammate as well as neighbor of Lobert's when he first came to the major leagues, the German-American Lobert earned the nickname "Hans" as a familiar form of Johannes, the German version of his given name, and was dubbed "Hans Number 2" by Honus Wagner. He would keep this name for the next 50 years. Lobert batted .274 for his career and played 14 seasons (1903, 1905–1917) with five National League clubs, including regular stints as a third baseman for the Cincinnati Reds (1906–1910) and Philadelphia Phillies (1911–1914). He also played with the Pittsburgh Pirates (1903), Chicago Cubs (1905) and New York Giants (1915–1917).