As the late 1970s unfold, Tim Templeton, an imaginative seven-year-old, is taken aback by the unexpected arrival of his baby brother, Boss Baby. This unusual infant sports a suit and tie whenever adults are around, mimicking their behavior with remarkable accuracy. Yet, when the adults are out of the room, the Baby’s demeanor transforms completely, showcasing a surprising blend of maturity and articulate conversation. Driven by curiosity, Tim devises a plan to capture the truth of this bizarre situation by recording a staff meeting led by Baby during an ostensibly innocent playdate. Unfortunately, his efforts come to a halt when Baby's associates catch him, resulting in the destruction of the damaging footage and a strict grounding for Tim.
As days pass, Baby slowly unfolds the reasons for his stay with the Templeton family. Utilizing the extraordinary powers of a special pacifier, both Tim and Baby gain insight into the enigmatic realm of BabyCorp, where extraordinary infants are trained for greatness. While most babies are lovingly placed in families, a few—those who lack a response to the joys of simple things like tickling—are redirected towards management. Here, they are infused with a secret baby formula that allows them to think and act like adults while maintaining perpetual youthfulness. As Baby’s agenda takes shape, he reveals his true mission: to investigate the troubling decline of affection for babies, driven by the skyrocketing popularity of puppies. His primary targets are none other than Tim’s parents, who unknowingly work for Puppy Co., the very company fueling this alarming trend.
As tensions escalate, Baby’s superior threatens to dismiss him unless he succeeds. This dire consequence would lead him to remain with the Templeton family and face the inevitable challenge of growing up alongside them. The boys are thus propelled into a frantic effort to avert this scenario. Their adventure takes an unexpected direction during Take Your Kid to Work Day at Puppy Co., where they inadvertently encounter the CEO, Francis E. Francis—who later turns out to be the disgraced former CEO of BabyCorp, known as Super Colossal Big Fat Boss Baby, ousted due to aging exacerbated by lactose intolerance. Francis is plotting to unleash a “Forever Puppy,” a creation designed to withstand the passage of time and eventually drain all love from babies, as he seeks revenge on BabyCorp.
While Francis embarks on a business trip to Las Vegas, he entrusts his brother Eugene with overseeing Tim's parents. In a comedic twist, Eugene transforms into a female nanny, yet the boys quickly unveil his ruse, making their escape with the help of playful neighborhood toddlers. Meanwhile, Francis prepares to launch his latest creation: Forever Puppies, adorable canines set to win the hearts of millions. However, Tim’s parents find themselves in a perilous situation trapped beneath a rocket.
A thrilling confrontation ensues as Tim and Baby (now grown as Theodore "Ted" Templeton) engage in a showdown on a catwalk, ultimately causing Francis to inadvertently plunge into a vat of mixer formula that reverses his aging cycle. Eugene reappears alongside the rejuvenated Francis, who, blissfully reduced back to infancy, joins Tim and Baby in rescuing Tim's parents from their dire fate and launching the Forever Puppies into space.
In the aftermath, Baby, now the CEO of BabyCorp, returns to the headquarters, confronting the decision to erase all evidence of his past adventures with Tim. Yet, a loyal employee hints at the possibility of Tim's memories being erased, but he firmly decides against this.
As the years pass, Tim and Ted realize that their connection has only deepened. They share a touching moment, reaffirming that love is not meant to be divided but rather cherished and nurtured by all parties involved. The narrative teases a new generation of Boss Babies, setting the scene as Tim’s eldest daughter anxiously awaits her newborn baby sister who is, quite fittingly, another Boss Baby in disguise.
