Tarbell started her career as a teacher but soon gave that up and began writing. She served as a writer and then managing editor of The Chautauquan, a monthly publication that supported the Chautauqua adult education movement.
She went to the Sorbonne in Paris to write a biography of Madame Roland, leader of an influential salon during the French Revolution, who was beheaded. In Paris, she also wrote articles for McClure's Magazine. That led to an editorship at the magazine, where she wrote a series on Abraham Lincoln, which revealed previously unknown details about his childhood in Kentucky and Illinois. Later, she wrote a popular series on Napoleon Bonaparte. In the process, she became a well-known biographer.
For her work on Standard Oil, Tarbell interviewed industrialist Henry H. Rogers, one of Rockefeller's associates at the company. Apparently Rogers thought Tarbell's piece would be complimentary and he was surprisingly candid about the company's unfair business practices. Tarbell's detailed research drew on company documents from throughout the nation (an unusual practice at the time), as well as interviews with former employees and competitors. It set the standard for investigative journalism of later years.
Her 19-part series appeared in McClure's Magazine beginning in November 1902. It revealed how the company engaged in spying and predatory pricing, struck cozy deal with railroads, and bought up competitors at bargain basement prices to create a monopoly over production, transportation, refining, and marketing of petroleum products. From Rockefeller, the series earned Tarbell the epithet Miss Tarbarrel.
In 1911, amid much public agitation about trusts, (Upton Sinclair's exposé of the meatpacking industry, The Jungle, had been published in 1906), the U.S. Supreme Court ruled that Standard Oil's practices violated the Sherman Antitrust Act and ordered the breakup of the company.
Tarbell's autobiography, All in Day's Work (1939) recounted her muckraking days (a term she abhorred) and other details of her life. Tarbell had a personal interest in the Standard Oil story. Her father was an early oilman, at first in the oil tank business, and later an oil producer and refiner, but was forced out of business by Standard Oil's unethical practices.