Pygmalion begins under a church portico in a rainstorm, where a crowd shelters and a man takes notes on everyone's speech. He is Henry Higgins, a professor of phonetics who can place any Londoner by their vowels. Among the crowd is Eliza Doolittle, a poor flower girl whose Cockney he mocks, and Colonel Pickering, a fellow language scholar. Higgins boasts that in a few months he could pass this girl off as a duchess at an ambassador's garden party.
The next day Eliza arrives at Higgins's Wimpole Street house wanting lessons so she can work in a flower shop. Pickering turns the boast into a wager: he will cover the costs if Higgins can really do it. Higgins takes the bet as an inspired folly and hands the bewildered girl over to his housekeeper to be washed and dressed. Eliza's father, Alfred Doolittle, a dustman who cheerfully calls himself one of the undeserving poor, turns up to bargain over her and delivers a comic defense of his own want of middle class morality.
Months of drilling follow. At a first social test in Mrs. Higgins's drawing room Eliza speaks perfectly but says shocking things, to general delight. By the climax she carries off the garden party, the dinner, and the opera, and the bet is won. But returning home that night, Higgins and Pickering talk only of their own relief that the bore is over, taking no notice of Eliza at all. Stung at being treated as a finished experiment rather than a person, she throws his slippers at him and walks out.
Eliza takes refuge with Mrs. Higgins, who understands her better than her son does. In the confrontation that follows, Higgins cannot see why Eliza is unhappy, since he treats everyone, duchess and flower girl alike, the same rough way. Eliza answers that Pickering's small courtesies, beginning with his calling her Miss Doolittle, were the real start of her self-respect, and that a lady is made by how she is treated. She refuses to crawl back, and finds that she can do without him.
Shaw adds a prose afterword explaining what becomes of everyone and rejecting the expected happy ending. Eliza does not marry Higgins; the bond between maker and made is, he argues, too one-sided for that. She marries the gentle, infatuated Freddy instead and sets up an independent life. The play, which Shaw calls deliberately didactic, ends with the created figure stepping off the pedestal and out of the creator's reach.