A final project for Life depicting the history of beef cattle in the Americas led Tom Lea to Mexico where he became fascinated with black fighting bulls. The artist turned to writing, and his first novel, The Brave Bulls(1949), became a bestseller and movie starring Mel Ferrer. Other works of fiction and history followed, including The Wonderful Country (1952), a best seller and movie starring Robert Mitchum; The King Ranch (1957) an annotated history of the mammoth South Texas Ranch; The Primal Yoke (1960), a mountaineering story set in Wyoming; The Hands of Cantu (1964), an account of horse training in 16th-century Nueva Viscaya; A Picture Gallery (1968), his auto-biography; and In the Crucible in the Sun (1974), about King Ranch properties in Australia. Lea illustrated all of his books and, in the case of The Hands of Cantu, he created portraits of the characters and hung them in his studio before writing the story.
During his lifetime, Tom Lea took pleasure in capturing portrait likenesses. He started with friends in El Paso and, when he went to war, drew well known subjects like Jimmy Doolittle, Claire Chennault, Berndt Balchen and Madame and Generalissimo Chiang Kai-shek. Lea reserved portraiture for his own pleasure, turning down offers of commissions. Lea wrote that "I select my subjects, they don't select me." Twice he made an exception to his rule, painting Benito Juarez 1948 and Sam Rayburn in 1966. Both portraits hang in public buildings in Washington, D.C.
The last mural Tom Lea completed was for the El Paso Public Library in 1956. Entitled Southwest, the painting was done as a gift for the citizens of El Paso by the artist, assisted by his wife Sarah. Lea's later years were devoted to the easel, in oil, watercolor, casein tempera, pastel and Chinese ink with landscape as the predominant subject landscape. Requests would come, resulting in paintings like Ranger Escort West of the Pecos for the office of Gov. John Connally; or The First Recorded Surgical Operation in North America: Cabeza de Vaca, 1535 completed for the Moody Medical Library, U.T. Medical Branch, Galveston. While these paintings hang in public buildings, almost all of Lea's work was delivered directly from his studio into the private collections of personal friends.
The first dinner given by Gov. and Mrs. George W. Bush in the Texas Governor's Mansion was to honor Tom Lea. The governor read from Tom Lea, An Oral History, recorded by Adair Margo, for friends that included Mrs. John Connally, Lady Bird Johnson, and the Kleberg family of the King Ranch. When accepting the Republican nomination for president of the United States in 2000, George W. Bush quoted Tom Lea about living on the "sunrise side of the mountain, " and, after his election, he made it known that a Tom Lea painting would hang in the Oval Office. Tom Lea died on January 29, 2001 following a fall at home. Laura Bush traveled to El Paso for the memorial service, the first trip she made as first lady of the United States. While in El Paso, she requested the loan of Tom Lea's painting Rio Grande from the El Paso Museum of Art to hang in the Oval Office.