In 1876, he obtained his PhD. with a dissertation on Gregorè the priest and the revolutionist. The first examiner for it was the historian, Georg Voigt. He completed his post-doctoral work in Leipzig in 1884, and became an associate professor in 1889 and a full honorary professor in 1891. He apparently had several doctorates: Karl Josef Friedrich (p. 130) even mentions five doctorates in his biography of Gregory. At least one doctorate in theology obtained in Leipzig in 1889 is attested.
In August 1914, Gregory, who had been a citizen of Saxony since 1881, enlisted in the German Army as its the oldest wartime volunteer. He became a second lieutenant in 1916 and fell in 1917 on the western front. He died on April 9, 1917 in a field hospital in Neufchâtel-sur-Aisne, France. Gregory specialized in NT textual criticism. He organized biblical manuscripts into a classification system (Die griechischen Handschriften des Neuen Testaments, 1908) which is the system in use throughout the scholarly world today. He is also credited with being the first to notice the consistent medieval practice (called Gregory's Law or Gregory's Rule) of collating parchment leaves so that grain side faced grain side and flesh side flesh side.