Randolph Jefferson (October 1, 1755 – August 7, 1815) was the younger brother of Thomas Jefferson, the only male sibling to survive infancy. He was a planter and owner of the Snowden plantation that he inherited from his father. He served the local militia for about ten years, making captain of the local militia in 1794. He also served during the Revolutionary War.

Randolph, known as "Uncle Randolph" when he visited Monticello, has been considered as a candidate for the father of Sally Hemings's children following DNA studies that found that the Hemings children descended from the Jefferson line. The theory that Randolph Jefferson fathered Hemings' children is not affirmed by the Thomas Jefferson Foundation, nor by most scholars of Jefferson. The Monticello Jefferson-Hemings Report (2000) determined that Thomas Jefferson was the likely father of Sally Hemings' children, though other scholars nonetheless contend Randolph is a strong candidate for paternity.^{[citation needed]}

Born at Shadwell, the Jefferson family plantation in Albemarle County, Virginia, his parents were Peter Jefferson, who died when Randolph was two years old, and Jane Randolph Jefferson. He was a twin to Anne Scott Jefferson and the only male sibling of Thomas Jefferson's to survive infancy. The twins were Thomas' youngest siblings, about 13 years younger than him. After Peter Jefferson's death, and while Randolph was a child, his affairs were managed by John Harvie Sr., the executor of Peter Jefferson's estate. After he died, his brother Thomas managed his affairs, such as his education and property, until he came of age in 1776. He assisted in management of his younger brother's affairs after 1776.

In 1764 and 1765, Randolph Jefferson studied with Ben Snead at the residence of his uncle Charles Lewis, Jr. and aunt Mary Randolph Lewis at Buck Island, which was a 960-acre tract located near Monticello and the Rivanna River in Albemarle County. He lived again at Shadwell with his mother in 1769, when he was taught by Patrick Morton. In 1770, the main house at Shadwell was destroyed in a fire, and his mother, Jane Randolph Jefferson, had a house built there as a replacement. He left Shadwell for Williamsburg when he was 16 to reside and study at the College of William & Mary from October 1771 until September 1772. He attended The Grammar School at the College of William & Mary and was tutored in higher subjects by Thomas Gwatkin, who taught mathematics and natural philosophy at the college. Additionally, he took violin lessons from Frances Alberti, as did his brother. Randolph Jefferson continued to “fiddle” throughout his life and willed his violin to his son, Robert Lewis Jefferson.

Thomas Jefferson described Randolph posthumously in a deposition that was taken as Randolph's sons contested the will that favored their stepmother, Mitchie Pryor Jefferson. Thomas was considerate and affectionate toward Randolph; they addressed each other as "Dear Brother," and exchanged visits and services with each other. Letters document that Thomas lent Randolph the harness for a gig, had his watch repaired, gave him a dog, sent him vegetable seeds, and gave him a spinning jenny. At Monticello, he was called "Uncle Randolph". A former Monticello enslaved man, Isaac Jefferson, recalled in 1847 that Randolph "used to come out among black people, play the fiddle and dance half the night..."

Historian Dumas Malone states that Randolph did not share his older brother's eloquence. His letters to Thomas show a disregard of grammar and the use of colloquialisms such as "tech" instead of "touch." His "rustic sense of humor" may have caused people to underestimate his intelligence, yet he lacked his brother's intellectual curiosity.

In 1776, Randolph Jefferson served in Captain Wingfield's Company of the Albemarle militia. He served with William Fossett and Joseph Nielson who had worked at Monticello and had live-in relationships with members of the Hemings family. He was a member of the local militia in 1779.

Along with his brother, Jefferson signed an Oath of Allegiance to the Commonwealth of Virginia in 1777, He, his brother, and Charles Lewis also signed the Albemarle County Oath of Allegiance to the Commonwealth on April 21, 1779. It was also called the Albemarle Declaration of Independence.