Kevin (Probably) Saves the World follows Kevin Finn, a cluelessly self-serving person who is on a dangerous path to despair. In a downward spiral, Kevin returns home to stay with his widowed twin sister and niece. On his first night there, an unlikely celestial being named Yvette appears to him and presents him with a mission – to save the world.
Kevin, who is on a dangerous path of despair, returns to his childhood home in Texas to crash with his widowed twin sister, Amy, and teenaged niece, Reese. It is a strained homecoming - he and his family have grown apart over the years - and Kevin has no real hope that anything will get better. But a series of fantastic events, including a meteorite landing near the house, lead Kevin to meet an unlikely celestial guide, Yvette. Yvette delivers incredible news to Kevin: in every generation there are 36 righteous souls on Earth whose mere existence protects the world. Kevin, she tells him, is the last of the 36 righteous. Humanity has been thrown into crisis. Without the 36, the world will begin to lose the one thing that allows us to persevere through the ups and downs of life: hope.
Yvette attempts to guide Kevin in his mission to help others, but when he tries to "help" a local brewer, Kevin's good intentions go horribly awry. Amy struggles to understand Kevin's strange behavior while still mourning the loss of her husband. Meanwhile, Kevin rekindles an old flame with unexpected consequences.
On his quest to become a better person, Kevin helps a young couple plan their wedding. In doing so, however, he sees the consequences of lies - both his own and the couple's. Meanwhile, Yvette attempts to organize the other celestial beings, and Reese witnesses her uncle's strange new talents first-hand.
When the universe leads Kevin to help Lucille - a mean-spirited diner owner - with some family drama, he quickly finds himself stuck in the middle of a tricky situation with her equally difficult sister. Meanwhile, Reese entertains the thought of Kevin having special powers, and Yvette begins to struggle with the side effects of being on Earth.