He became professor of philosophy in the University of Munich, and while professor he published books on Aristotle (1871) and on Albertus Magnus (1880). From 1875 to 1890, and again from 1893 to 1912, he was a member of the Reichstag, and after 1909 led for a time the Centre (Catholic) Party in that assembly. In 1891, the Regent of Bavaria made him a life member of the upper house of the Bavarian Landtag.

As leader of the largest party in the Bavarian Landtag, in 1912 Hertling was appointed Bavarian Prime Minister and Minister for Foreign Affairs by Luitpold, Prince Regent of Bavaria. King Ludwig III later elevated him to the rank of Count. Following the outbreak of World War I, Hertling supported the policy of Chancellor Theobald von Bethmann Hollweg but declined to become his successor. Hertling became German Chancellor and Prime Minister of Prussia only after the fall of Georg Michaelis in 1917 but was incapable of meeting the crisis during the final stage of the war. Due to his age and conservatism he was unable to overcome the power of the military high command, led by Paul von Hindenburg and Erich Ludendorff, despite having been a deputy to the Reichstag and a leader of the Centre Party. He was required to resign his seat when he took office under the Kaiser.

He founded the important German Catholic fraternity Askania - Burgundia and was a member of K.St.V. Arminia at Bonn. His great - granddaughter is actress Gila von Weitershausen.