At a shareholders meeting for International Projects, a billion-dollar corporation, John T. Blessington announces that he is replacing Edward L. McKeever, the company's founder, president and chairman of the board who is resigning to serve as Secretary of Defense in Washington D.C. Laura Partridge, Judy Holliday, a stockholder with just ten shares, infuriates the company's arrogant, self-serving executives by repeatedly exercising her right to ask questions during the meeting.
Blessington devises a plan to hire Laura for the meaningless position of director of shareholder relations in order to keep her occupied and out of the executives' business. He assigns her a secretary named Amelia Shotgraven, Neva Patterson, with secret instructions to obstruct Laura as much as possible. With no substantial job duties, Laura begins to write letters to the stockholders. She gains Amelia's friendship and assistance by helping her develop a romantic relationship with the office manager.
When the directors discover that Amelia is helping Laura, they fire Amelia. However, Laura discovers Blessington's unqualified brother-in-law Harry Harkness has driven an apparent competitor into bankruptcy, unaware that International Projects actually owns the smaller company. With that as leverage, she gets Amelia rehired.
Still determined to neutralize Laura, the board sends her to Washington to persuade McKeever to award them some government contracts. She agrees to go, but secretly intends to convince McKeever to return and retake control from the crooked board even though, when assuming his Cabinet position, he had sold his shares in the company to avoid any conflict of interest. After Laura tells him about Harry's blunder, McKeever agrees to leave his government post and try to wrest control of the company. However, Blessington and his men block his attempt, and Laura quits.
McKeever takes the company to court, arguing that sending Laura to persuade him violated the lobbying laws, as she was not a registered lobbyist. When Laura is forced to admit on the stand that she had a romantic reason for seeing McKeever, the judge throws the case out. However, many of the smaller investors with whom Laura had forged relationships through her letters have sent her their proxy votes, granting Laura the right to vote their shares. Laura and McKeever use these votes to replace the entire board. At a meeting of the new board, it is revealed that Laura has married McKeever.
For its final scene, the film changes from black-and-white to color, showing the small stockholders' wedding gift to Laura, a gleaming solid gold Cadillac that she drives around Manhattan.
