Attorney Don Thomas, who joined the firm in 1944, developed a close, personal friendship with Johnson and, when Looney suffered a stroke in 1958, succeeded Looney in overseeing Johnson's legal matters. Subsequently, Thomas became more than the family's business attorney by serving as president of the LBJ Company until his retirement in 1990.

Other notable attorneys joined the firm during the '40s. Martin Harris, a UT law school graduate, came on board in 1947. He would become one of the state's leading attorneys in water rights. The following year, Dean Moorhead, who had graduated from Columbia Law School with the highest grade point average on record at the time and was a recipient of all three awards given to graduating seniors, left the Attorney General's office to join the firm, which was then renamed Looney, Clark & Moorhead. Frank Denius, one of the most highly decorated soldiers during World War II, was hired in 1949.

In the '50s, Charles Mathews joined the firm. He had been the first assistant attorney general at the time administrative law was in its infancy. He participated in its development and achieved a then-unparalleled degree of expertise. As the practice of law became more specialized, he concentrated on transportation law, ultimately leaving the firm to become president of Red Ball Motor Freight. He subsequently became a state district judge until retirement.

In 1955, Mary Joe Carroll became the first woman hired to practice law full-time by a major firm in Texas. Carroll, who scored highest in the state the year she took her bar exam, worked with Looney in the firm's appellate practice. She also served as parliamentarian for Lt. Governor Ben Ramsey in the Texas Senate. This experience, in part, caused her to be selected to draft legislation for clients, including both the Open Meetings Act and the Open Records Act.

Looney died in 1962, Clark in 1992. Had Looney lived as long as Clark, he would have been amazed at the growth and specialization that occurred at the firm. Charles Mathews called Looney "the last complete lawyer."

He also maintained his banking interests as a member of the board of directors of several banks and his interest in educational and historical endeavors, including his service on the boards of Southwestern University, the University of Texas, and the Texas State Historical Association.

The firm that began as Looney and Clark became Clark, Thomas & Winters, a Professional Corporation, in 1993. As of August 2010, the firm has 85 attorneys with a total of 190 employees, providing quality comprehensive legal services to its clients. The firm's practice areas include antitrust, appellate, banking, business law (corporate, federal tax, securities and intellectual property), energy and telecommunications, health care law, insurance, labor and employment law, product liability defense, state and local taxation, and wills and estates.