His parentage is unknown, but the Elisabet Ney Museum relates the possibility that he was the son of Isabella Davidson (or Montgomery) and a prominent Scottish jurist, Duncan McNeill, 1st Baron Colonsay.

[3] In 1852, Montgomery studied medicine at the University of Heidelberg, where he did lab work under Robert Bunsen and came under the influence of Christian Kapp, Ludwig Andreas Feuerbach and Jacob Moleschott.

After being diagnosed with tuberculosis in 1863, Montgomery left the Royal College of Physicians of London and established medical practices on the resort island of Madeira (1863–1865), in Menton (1866) on the French Riviera, and also in Rome (1867) and Munich (1868), while continuing to do his research.

He was an advocate of humanitarianism and a "religion of life," focusing on the idea that man must not ignore the potential of his own yet-to-be-completed evolutionary process.

[8][9] While a student at the University of Heidelberg in 1853, Montgomery began a courtship with sculptor Elisabet Ney, who was visiting friends in the city.

Montgomery received a letter from his friend, Baron Carl Vicco Otto Friedrich Constantin von Stralendorff of Mecklenburg-Schwerin, who had moved to Thomasville, Georgia, with his new wife, Margaret Elizabeth Russell of Boston, Massachusetts, declaring the location "Earth's paradise.

"[10] On January 14, 1871, Ney and Montgomery, accompanied by their housekeeper, Cenci, emigrated to Georgia, to a colony promoted as a resort for consumptives.

With the help of German Consul Julius Runge in Galveston, Ney was shown Liendo Plantation near Hempstead in Waller County.

He served two terms as Waller County Road Commissioner and oversaw the building of an iron bridge across the Brazos River.