In the early 1930s Lovell shared a studio space in New York with Harry Anderson and Al (Nick) Carter. He eventually moved to the artist colony of New Rochelle just outside New York City. New Rochelle was home to a number of other illustrators, including Norman Rockwell and Mead Schaeffer.
After 1936, Lovell progressed into providing illustrations for advertising agencies and slick magazines such as Redbook, Life, Collier's, The American, Woman's Home Companion, and Cosmopolitan. From 1940 onwards Lovell produced covers for several magazines including Ace-High Western, Clues, Complete, Detective Tales, Dime Detective, Rangeland Romances, Star Western, and Top-Notch. He also drew pen and ink interior illustrations for The Shadow, Courtroom Stories, Popular Western, Triple Western, and Clues.
Lovell served for two years in the Marine Corps Reserve during World War II. He was sent as a Staff Sergeant to Washington DC with John Clymer and Fred Lasswell to illustrate the Marine Corps magazine, Leatherneck.
On returning to Westport Lovell produced a set of historical drawings for National Geographic Magazine, including depictions of the Norman invasion of England, the career of Alexander the Great, and the conquests of the Vikings. He took great care in reproducing what he considered to be historical accuracy in the illustrations, including making models of weapons and ships, visiting historical sites and carrying out other research. He was also commissioned to create a series of paintings about Western oil exploration, as well as several paintings for the Church of Jesus Christ of Latter-day Saints.
In 1969, under commission from the Abell-Hanger Foundation, Lovell produced a series of paintings commemorating the history of the Southwest that are now on permanent display at the Permian Basin Petroleum Museum, Midland, Texas. These works, a historical series about Native Americans, represent a turning point in the subject matter of Lovell's work. From this point on he concentrated on depictions of Native American life, exploration of the West, and Western art.
In 1973, he was invited to become a charter member of the National Academy of Western Artists, and is the only artist to twice receive their Prix de West Award. In 1974, he was elected to the Society of Illustrators' Hall of Fame, and in 1975, became a member of the Cowboy Artists of America. In 1992, he received the Robert Loughweed Award from NAWA as well as their Lifetime Achievement Award. In 1994, he displayed several pieces at the National Academy of Western Artists Show in Oklahoma City.
The Tom Lovell Collection of personal letters, photographs and scrapbooks containing tear sheets of his completed paintings is currently held at the Norman Rockwell Museum Archives' Reference Center Collection. In 2006, the NRM put several of Lovell's paintings on display as part of the exhibition "National Geographic: The Art of Exploration".