Monty Brewster, a down-on-his-luck minor league baseball pitcher, finds out he is the sole living relative of a deceased great-uncle, a multimillionaire who has left him an unusual inheritance challenge. To inherit the full $300 million, Brewster must spend $30 million in 30 days without acquiring any assets; if he fails, he will be left with nothing. The conditions explicitly prohibit him from revealing the challenge's terms to anyone else or donating more than a small fraction of the money to charity or to individuals. Brewster initially sees the task as easy, eagerly embarking on the challenge with his best friend, unaware of the difficulties ahead.

As Brewster progresses with the challenge, his extravagant spending spree catches the public's eye, making him an overnight celebrity. Yet, the endeavor proves more complicated than expected. He encounters numerous obstacles, including the suspicion of those around him who question his sudden, irrational financial behavior. The conditions of the will force him to innovate in wasting the money without showing for it, leading to a series of comedic endeavors that strain his relationships and challenge his understanding of money's value and the true nature of happiness.