He attended public schools in Cambridge, Massachusetts, and studied abroad with a tutor for a year in Athens, Greece.

Thayer served as Secretary to Justice Horace Gray, U.S. Supreme Court in 1892.

He practiced law in Boston with the firm of Brandeis, Dunbar, and Nutter from 1893–1900.

In 1910, Thayer was appointed as Dean of Harvard Law School, succeeding James Barr Ames, who had died in January of that year.

[2] Cole Porter, the famous American songwriter, was enrolled in Harvard Law School in 1913.