Hill's entrepreneurship and engineering aptitudes became apparent at an early age. He was a hard worker and began earning his way early on. At first, he earned money by helping his mother with household chores, and he soon graduated to his own newspaper route. In order to earn additional funds, Hill began delivering coal and firewood to local homes in San Francisco area, an arduous job considering the heavy loads he had to carry up and down the hills. In San Francisco, Hill had a workshop at the back of his home where he built and designed electric motors, a wireless radio, and various other mechanical devices. His friends learned at an early age of Hill's engineering skills when he built an electric-shock machine and dared them to hold onto the conducting rods for as long as possible.

Upon graduating from Berkeley High School in 1912, Hill began searching for an engineering job. He wanted to work for the Hall-Scott Motor Company but, at first, he was turned down. Nevertheless, Hill persisted in seeking employment from the company, and was finally offered a job by Hall-Scott on January 29, 1913. Hill realized that a college education was necessary for his career, and he entered the University of California at Berkeley in 1913. He continued to work at Hall-Scott Motor Company and at his engineering education until the United States entered World War I. On the first day, after the United States' declaration of war, Hill enlisted as a regular seaman with an application pending for officers' training in aviation.

Unfortunately, Hill did not hear from the Navy after his enlistment, except for a letter which directed him not to leave the 12th Naval District. While he waited for his call to duty, Hill completed his senior thesis for his bachelor's degree in engineering. During this time, Hill was charged with establishing a course in airplane instruction and demonstration for the Army Air Corps' ground school at the University of California at Berkeley. Hall-Scott engines and other various engines were provided to him, and he wrote instructional materials to demonstrate how the engines operated.

In the meantime, Al Hall, President of Hall-Scott Motor Company, was put in charge of designing and building the new 12-cylinder engine for airplanes. Hall asked Hill to join his staff and help design the new engine. On April 6, 1918, Hill received orders to immediately report for duty at the Boston Naval Headquarters. Nevertheless, Hill's Navy career was short-lived. Al Hall needed Hill to continue his work on the Liberty 12 engine, and Hall was able to get Hill discharged from basic training and sent back to Dayton, Ohio to continue his work. Unfortunately, Hill never returned to basic training in the Navy as he had hoped and spent the rest of the war working for Al Hall.

After World War I, Hill held a variety of jobs including a few of his own entrepreneurial adventures. Although Hill wanted to return to the aviation industry, his dream did not become reality until 1928, when Ray Acres, a longtime friend, recommended Hill to the company that was to be Lockheed Aviation's new eastern distributor. The company was Air Associates, a airplane sales and equipment distribution company. Hill began working for Air Associates in 1928, and the company grew and expanded rapidly.

By 1938, Hill had been promoted to president of the company. In this year, Air Associates had their first encounter with labor unions, specifically the C.I.O. At first a small group of Air Associates' employees organized and tried to get an exclusive bargaining contract with the company. Hill and the company refused to sign the C.I.O. contract, and when the Air Associates dismissed a few employees for undesirable behavior, the C.I.O. filed charges with the National Labor Relations Board (NLRB). (The NLRB was established by the National Labor Relations Act, or Wagner Act, to negotiate and settle labor problems.)

After the 1938 dispute was settled, the union activity in the Air Associates= plants was minimal until 1941. In 1941, Air Associates relocated its headquarters to Bendix, New Jersey. On June 17, 1941, a C.I.O. representative approached Air Associates' management and demanded a union contract be signed by the company. The company refused but agreed to a general election for union representation. At this point, events began to escalate rapidly. On July 3rd, Air Associates laid off nine men in the sheet metal department because of an aluminum shortage. On July 8th, the C.I.O. presented its contract to the company, and before any negotiations could take place, the C.I.O. called a strike because of the nine men that had been laid off. Air Associates refused to bargain with the strikers, and on July 17th, the strike turned violent. The N.L.R.B. intervened and, through mediation, settled the strike by July 22, 1941.

Though the immediate problem had been settled, Hill and the company still refused to bargain with the C.I.O. By October, the situation was strained, and on October 23, 1941, 2,000 to 3,000 picketers descended upon Air Associates. Due to Hill's hard-line position against the unions, Franklin D. Roosevelt, President of the United States, ordered the seizure of all Air Associates' plants on October 30, 1941. The conditions established by the war department for the plants' return to company control was the removal of Hill as president and the removal of Vice-President Harold Crow. On November 19, 1941, the Board of Directors of Air Associates removed Hill as president of the company.

While at Air Associates, Hill met his second wife, Ellen Mayo Hill. Over the next ten years, the couple would observe the birth of five daughters: Ellen (Nellie), 1942; Marcia, 1944; Holly, 1945; Elizabeth, 1949; and Isabella, 1952. Shortly after his removal from Air Associates, the United States entered World War II. Hill, and his family moved to Rockford, Illinois, where Hill established various small companies that supplied aviation parts to the U.S. government. By the end of the war, Hill was established as an entrepreneur.

Hill's entrepreneurial abilities began to expand after the end of the war. In 1945, Leroy started the Hill Machine Co., later renamed the Hill-Rockford Co. This company was to become the focal point of his life, and he remained in control of the company for the rest of his life. Although Hill-Rockford Company was the primary business entity, Hill invested in or manage numerous other companies: Aldrich Co.; Polo Pump Co.; Rystrom Engineering; Syncro Flame, Inc.; The Walter E. Selck Co.; Vance Industries; Ponder Oil Ltd.; and many others.

After the 1940s, Hill began to focus more attention on the political and philosophical issues that affected his life. Throughout the 1950s and 1960s, Hill wrote his congressmen on a regular basis, expressing his concern about the role of government and other national issues. Besides writing to his congressmen, Hill also contributed financially to various political organizations, although his primary interests were organizations concerned with the economy and economic issues. In addition to his correspondence concerning political organizations and issues, Hill also wrote letters expressing his support and concern to business leaders who were faced with labor problems similar to those he encountered at Air Associates.

Hill led a long and adventurous life. Although he was forced to slow down after a stroke in 1976, he continued to express his opinion and to lead a full life until his death in 1981 at the age of 87. There is no single word that can accurately describe the life and beliefs of F. Leroy Hill. Perhaps the best description of his life came from his wife, Ellen. In 1992, while Dr. Craig Miner was preparing to write Hill's biography, Ellen Hill commented "that her husband was a happy man, secure in what he believed to be right."