Bobbie Walters, a cab driver in a Midwest city who is trying to save enough money to marry his sweetheart, Dorothy Wright, an attendant at the cigar and newspaper counter of a large hotel, is able to amass $15,000. He acts like a millionaire and soon is fleeced of the money by two Wall Street swindlers. Broke, Bobbie is forced to work as a bellboy at Dorothy's hotel. After a series of struggles and adventures, Bobby wins a fortune in the oil fields of Louisiana, despite the efforts of his rivals, who dynamite his oil derricks.

A typographer makes a mistake by printing the winning number of the national lottery. Many people believe they have won the jackpot. Pursued by his newspaper editor, the worker appears in court where all mystified people are invited to testify.

Millionaire for a Day was filmed during the summer of 1925 in Skåne, the southernmost province of Sweden. This Edvard Persson's third film became a flop in Stockholm, but was quite successful in many rural areas all over the country.