Seven-year-old Tim Templeton enjoys a comfortable life as an only child, basking in the undivided love and attention of his parents. His world turns upside down when his new baby brother arrives. This is no regular baby — he's a suit-wearing, briefcase-carrying infant with an adult-level intellect and a mysterious agenda. Tim is initially bewildered and jealous of the attention the baby receives, but he soon becomes suspicious of his peculiar behavior, particularly the infant's unusual business-like demeanor and ability to speak like an adult.

The baby, known as the “Boss Baby,” reveals that he has been sent on a secret mission by BabyCorp, an organization responsible for the management and love distribution to babies. He informs Tim that a new puppy product by Puppy Co. threatens to overshadow babies in the cuteness market, potentially reducing the love for babies across the world. Realizing they need to cooperate to maintain the balance of love between puppies and babies, the two brothers embark on a comedic adventure. Their sibling rivalry slowly turns into a genuine bond as they work together to infiltrate Puppy Co. and thwart the plans that could upend the love equilibrium between babies and puppies.