Though Will Hunting (Matt Damon) possesses extraordinary intelligence, including an exceptional knack for memorizing information and intuitively proving complex mathematical theorems, he leads a modest life as a janitor at MIT, residing in a meager apartment in a struggling South Boston neighborhood. As a victim of child abuse, Will harbors deep-seated self-loathing stemming from his troubled childhood, which manifests as self-sabotage in both his career and love life, preventing him from keeping a steady job or forming lasting romantic relationships.
During his first week at MIT, Will astounds everyone by solving a formidable graduate-level math problem left on a chalkboard by Professor Gerald Lambeau (Stellan Skarsgard), a renowned Fields Medalist and Combinatorialist, who had hoped students might tackle it by semester's end. The entire MIT community is abuzz with curiosity about the identity of the problem solver. Lambeau, mistakenly believing Will is vandalizing the board, chases him off, only to later discover that Will has indeed solved the problem correctly. Intrigued, Lambeau seeks out Will.
Amidst personal turmoil, Will finds himself in a confrontation with a childhood bully, leading to his arrest after an altercation with a police officer who intervenes. Recognizing Will's immense potential to become a brilliant mathematician akin to Evariste Galois, Lambeau intervenes at Will's trial, offering him a critical choice: serve time in jail or work under Lambeau's guidance, which includes studying mathematics and undergoing therapy. Will reluctantly chooses the latter, albeit with skepticism about the need for therapy.
Initially, five psychologists fail to establish a connection with him. In a last-ditch effort, Lambeau brings in his old friend and fellow MIT classmate, psychologist Sean Maguire (Robin Williams), who hails from the same neighborhood as Will. Unlike the others, Sean challenges Will’s defenses and engages him on a profound level. At one pivotal moment, Will critiques a watercolor painting that Sean created, revealing Sean's buried emotions regarding the loss of his wife. Sean reacts strongly, grabbing Will and threatening to derail his chance at recovery, yet this exchange lays the groundwork for a unique therapeutic relationship.
In subsequent sessions, Will is deeply impacted when Sean recounts how he forfeited his ticket to Game 6 of the 1975 World Series to spend precious moments with a stranger who eventually became his wife. This story encourages Will to contemplate a relationship with Skylar (Minnie Driver), a woman he met at a bar near Harvard, fostering further intimacy between them.
However, their relationship is not one-sided; both Sean and Will push each other to confront their fears. Sean struggles to move on after his wife's death, while Will battles his issues, sticking to the defensive mechanisms he relies on in life. Meanwhile, Lambeau’s pressure for Will to excel becomes overwhelming, culminating in Will's refusal to attend promising job interviews arranged by Lambeau, leading to tensions between them.
A turning point occurs when Will witnesses an argument between Lambeau and Sean, forcing him to recognize that the situation is not simply Will against the world; these mentors are human and flawed as well. When Skylar proposes moving to California for medical school, panic grips Will; her well-meaning references to his burdened past trigger emotional turmoil, prompting him to flee in frustration.
Sean highlights Will's patterns of preemptively sabotaging his relationships to evade the emotional pain of failure. This introspection becomes the catalyst for Will's breakthrough during another therapy session, where he confronts the trauma they both endured as victims of abuse. Sean's gentle refrain, "It's not your fault," eventually resonates with Will, breaking through his defenses.
With renewed resolve, Will decides to reclaim his life. For his 21st birthday, he receives a refurbished Chevrolet Nova from his friends, spurring him to pursue a new life with Skylar instead of settling for lucrative job offers. Leaving a heartfelt note for Sean—using one of Sean's own famous lines, “I had to go see about a girl”—Will embarks on a journey to reunite with Skylar, embracing an uncertain but hopeful future.
As Sean prepares to travel the world and reconcile with Lambeau, the movie concludes on a poignant note when Chuckie (Ben Affleck), Will's best friend, finds that Will has finally taken the leap he longed for: a chase towards a better life, revealing that sometimes, moving forward means facing one's fears and choosing love over comfort.
