Thompson was born to Lewis Oliver Thompson and the former Flora Lee Agnes Murray in Alvord in Wise County in what is now part of the Dallas-Fort Worth Metroplex. When he was ten years of age, his family moved to Amarillo, where the senior Thompson, operated a drug store. Thompson was already a successful entrepreneur even as a teenager. He graduated from Amarillo High School and attended Virginia Military Institute in Lexington, and later the University of Texas at Austin, where he earned a law degree.
During the Great War, Thompson became an expert in machine-gun tactics. In the Meuse-Argonne campaign, he worked out a mass machine-gun firing technique and attained the rank of lieutenant colonel, having received a battlefield promotion from General John J. Pershing. At twenty-six, he was the youngest lieutenant colonel in the Army. After the cessation of hostilities, Thompson remained in Europe to direct the stockpiling of German weapons with the Army of Occupation.
In 1919, he was among the organizers of the American Legion, which lobbies for various veterans’ causes. That same year, he attended the Paris Peace Conference, where U.S. President Woodrow Wilson headed the American delegation, which also included Edward M. House, a rice magnate from Houston.In 1936, Thompson was named colonel of the Texas National Guard. He was promoted to commanding general in 1952 and was thereafter known as "General Thompson” though his biographer refers to him as "colonel".
On his return from Europe to Amarillo, General Thompson practiced law and owned the Amarillo and Herring hotels. He maintained a penthouse suite atop the Amarillo Hotel, where he resided. The hotel was built in 1889. Laura Vernon Hamner, a West Texas ranch historian, former school superintendent, and well-known civic leader, lived in Thompson’s Herring Hotel for many years. Thompson patronized the western artist Harold Dow Bugbee, a curator of the Panhandle-Plains Historical Museum in nearby Canyon. He also built the first multi-story office building in Amarillo, called simply the Amarillo Building.
In 1924, Thompson married the former May Esther Peterson (October 7, 1880—October 7, 1952), a Wisconsin native and a star of the Metropolitan Opera in New York City who was twelve years his senior. The couple met in the First Methodist Church of Amarillo, where Thompson was her escort for a performance. In addition to the hotel suite in Amarillo, the couple lived in the capital of Austin during much of the time that Thompson served on the Railroad Commission. They also maintained a summer home in Estes Park, Colorado. They had no children. Mrs. Thompson died suddenly on her 72nd birthday.
Thompson thereafter married Myda Bivins (1892–1978), the widow of Miles Bivins, a prominent Amarillo cattleman. Lee Bivins, the father of Miles Bivins, had been Thompson’s predecessor as mayor, having died in office after four years of service. Hence, Thompson’s second wife was the former daughter-in-law of the man who had preceded Thompson as mayor.
Though Thompson was a Democrat, the Bivins family became prominent Texas Republicans as the state adopted a two-party system. Former State Senator and U.S. Ambassador to Sweden Miles Teel Bivins of Amarillo was a grandson of the late Miles and Myda Bivins.
Thompson was elected to the nonpartisan position of mayor of Amarillo in 1928 on a platform advocating the reduction of utility rates. On taking office in 1929, he established a competing municipal natural gas company and launched a successful consumer boycott of telephones to persuade the companies to lower rates.He also launched a major capital improvements campaign. He served as mayor for two two-year terms, until 1932, when he was appointed by Governor Ross Sterling, a founder of the future Exxon Company, to the Texas Railroad Commission. A vacancy occurred when commissioner and former Governor Pat Morris Neff resigned to become the president of Baylor University in Waco.
On the commission, Thompson built his reputation as an oil and gas expert. He was elected to full six-year terms in 1936, 1942, 1948, 1954, and 1960. He resigned two-thirds into his last term, and Governor John B. Connally, Jr., named Byron M. Tunnell, former Speaker of the Texas House of Representatives as Thompson’s successor. Tunnell's departure from the House paved the way for Ben Barnes to become the youngest Speaker in Texas House history.
Under Thompson's guidance, the Railroad Commission developed conservation and production measures that brought order to the chaotic East Texas oil field in the 1930s, where oil prices fell from $1.10 to 10 cents a barrel.
Thompson long opposed nationalization of the petroleum industry and worked to establish the Interstate Oil Compact, having served three terms as chairman of the group. He was one of the first to warn the industry against reliance on imports in time of war, a prophecy which bore fruit with the Gulf War of 1991 and the continuing War on Terrorism.
In 1937, U.S. President Franklin D. Roosevelt sent Thompson to the World Petroleum Conference in Paris, France. With the outbreak of World War II, Thompson briefly rejoined the Army before returning to Texas to ensure oil supplies for Allied forces.
In 1951, Thompson was honored by several trade associations: the Texas Independent Producers and Royalty Owners Association, the Society of Petroleum Engineers, the Texas Mid-Continent Oil and Gas Association, the Independent Petroleum Association of America, and the American Petroleum Institute, which awarded him the "Gold Medal for Distinguished Achievement."
Thompson did much to enhance the credibility of the Railroad Commission, which had been created in 1891 during the first administration of Governor James Stephen Hogg. He and his wife relocated to Austin, where the commission meets and conducts its business. He tried to build public support for Railroad Commission services. At every opportunity, he promoted Texas oil and the idea that regulation would enhance, not hamper, the free-market. Regulations, however, increased the price of oil by holding back production but promised steady supplies in the future.
Both the petroleum conservationists and the major oil companies received a system of mandated oil-production levels known as prorationing. The Railroad Commission determined how much oil could be produced monthly in accord with market demand. This practice permitted price-fixing by major oil companies and conservation of Texas’ reserves. The tens of thousands of independent oilmen who owned most of the East Texas fields opposed prorationing but were reconciled to Thompson’s system when they realized that the commission would allow narrow spacing of wells, a policy which favored the smaller independent producers.
In 1930, the Railroad Commission employed 69 persons; by 1939, it had 566 employees working in multiple divisions. Thompson sought to hire new graduates from the state’s geology and petroleum engineering schools. He knew nost of those young people would move to higher-paying jobs in the private sector. However, he believe that they would promote the mission of the Railroad Commission because of their prior employment.
In 1944, Thompson moved to protect Texas interests by leading the opposition to the Anglo-American oil treaty in the Middle East. This pact would have formed a commission dominated by the major oil companies to assess post-war demand for Mideast oil and authorized production quotas. Thompson, Interior Secretary Harold L. Ickes, and the independent oil companies opposed the idea of giving the major companies so much control over global marketing and production. The treaty eventually failed, but the competition from Mideast oil would continue.
Thompson twice ran for governor of Texas, having lost the Democratic nomination both times to W. Lee O'Daniel, a populist radio announcer and salesman originally from Ohio and later Kansas. Thompson was believed to have been the leading candidate in 1938 until O’Daniel made his last-minute entry. O’Daniel won the nomination, 573,166 votes (51.4 percent ) to Thompson’s 231,630 (20.8 percent). The remaining 27.8 percent was divided among eleven other candidates. In the 1940 primary, held when the state had two-year gubernatorial terms, Thompson offered proposals of aid to labor, the establishment of a public utility commission, and a nickel-a-barrel oil tax to pay for the state's old-age pensions. He noted that Texas oil was not limitless and was taxed less than was oil in several other states. Nevertheless, Thompson again finished second to O’Daniel, 645,646 (54.3 percent) to 255,923 (21.5 percent). Also in the race was controversial former Governor Miriam Ferguson, who received 100,578 votes (8.5 percent). The remaining 15.7 percent was divided among four other candidates."Pappy" O’Daniel, as he was known, resigned in his second abbreviated term and narrowly won a special election to the United States Senate, having defeated then U.S. Representative Lyndon B. Johnson, on the death of Senator Morris Sheppard of Texarkana.
Thompson served on the boards of Texas Tech University in Lubbock and his alma mater, VMI. He was a member of St. Andrew's Episcopal Church, the Masonic lodge, the Shriners, and the Amarillo Rotary Club.
On his retirement from the Railroad Commission, the Texas State Legislature designated the former Tribune Building as the Ernest O. Thompson Building at Colorado and West Tenth streets. It was the tallest building constructed in Austin during the 1940s.
After Thompson’s death, the Texas Historical Commission placed a marker to honor him in the Thompson Park, which the city had already named for its former mayor. The park, located off Dumas Drive in north Amarillo, houses Wonderland Amusement Park, a small zoo, a lake, a ball park, a golf course, and facilities for picnicking.
James Anthony Clark penned the biography of Thompson, Three Stars for the Colonel: A Biography of Ernest O. Thompson in 1954. It was published by Random House in New York City.
Thompson is buried in the Texas State Cemetery in Austin beside his first wife, May. In 2001, Thompson was incuded among the "100 Most Influential People of the High Plains", as compiled by the Amarillo Globe-News.
Overall, Thompson’s main legacy is perhaps his dogged attempt to keep his state's oil-based wealth within Texas.In 1957, Sam Rayburn of Texas, Speaker of the United States House of Representatives, told a U.S. Senate committee which was investigating a shortage of American oil production at the time, that “in my humble opinion, the general knows more about oil than any [other] man in the world." Thompson used the occasion to explain how Texas policies had deliberately reduced production to benefit the independent oil producers. The lack of production, moreover, he maintained, was "a myth.