Thomas had studied in Britain under John Ruskin and Dante Gabriel Rossetti, members of the Pre-Raphaelite Brotherhood.
Farrer emigrated to America in 1863 and opened a studio in New New York In his first years as a professional artist in the 1860s, Farrer painted Pre-Raphaelite still lives, some landscapes and marine works, and also began his first efforts at etching. In the 1870s, Farrer"s landscape work shifted to the tonalist style for which he is best remembered.
He co-founded the American Watercolor Society and, unlike most artists of the time, painted in water colours almost exclusively.
His tonalist landscapes, which he continued to create into the 1890s, typically depict a misty or cloudy landscape with a marsh or small pond in the foreground. The sun is often setting in a Farrer painting, and the overall feeling one of stillness.
During the same period, Farrer became a driving force in the Etching Revival in America. Farrer"s best known etchings depict New New York
He etched a series of street scenes in the 1860s, and another series of New York Harbor scenes in the late 1870s and 1880s.
Farrer is buried in Brompton Cemetery, London.
He was a founding member of the New York Etching Club in 1877, and active in the promotion of etching as a creative medium rather than a reproductive one.