A gardener by trade, Sam seemed to be a simple Hobbit of plain speech. However, his love for Elves, his gift for poetry, and his belief that the world contains greater wonders than most hobbits are aware of (all nurtured by his tutor Bilbo Baggins) set him apart from the beginning. It was Sam who first introduced the theme of the Elves' sailing from Middle-earth, a subtle foreshadowing of Bilbo and Frodo's final journey across the Sea. He lived with his father, Hamfast Gamgee, better known as "The Gaffer", on Bagshot Row in the Shire, close to Bag End. Sam's mother was Bell Goodchild; he had five siblings: Hamson, Halfred, Daisy, May, and Marigold.

As "punishment" for eavesdropping on Gandalf's conversation with Frodo regarding the dangers of the One Ring, Sam was made Frodo's first companion on his journey to Rivendell in the beginning of The Lord of the Rings. Sam saved Frodo's life more than once during the quest to destroy the Ring, and he accompanied him all the way to Mount Doom.

After Shelob attacked and seemingly killed Frodo, Sam took the Ring, intending to complete the quest. Because he held the Ring for a time, he is considered one of the Ring-bearers.

After the War of the Ring, he married Rose "Rosie" Cotton back in the Shire. They had thirteen children: Elanor the Fair, Frodo, Rose, Merry, Pippin, Goldilocks, Hamfast, Daisy, Primrose, Bilbo, Ruby, Robin, and Tolman. After Will Whitfoot resigned his post as Mayor of Michel Delving (the largest town in the Shire and the "unofficial capital"), in Fourth Age 7, Sam was elected Mayor of the Shire for seven consecutive 7-year terms.

After his wife died in Fourth Age 61, Sam entrusted the Red Book to Elanor and left Middle-earth to sail across the Sea and be reunited with Frodo in the Undying Lands, (though it should be noted that as they were both born mortals, they would still eventually die a mortal death).