One of Banneker's crowning moments as an inventor came as a young man, he invented a clock made entirely out of wood that kept perfect time for the next forty years. It is believed that this clock was the first to be made completely in America. From his work on this clock, he began to fix watches, clocks, and sundials. His fascination with clock work created a greater interest in mathematics and astronomy.

In 1791, Major Andrew Ellicott asked Banneker to help him survey the "Federal Territory", which would become the nation's Capital. Working alongside, Pierre L'Enfant, Banneker became an expert on the plans for the city. L'Enfant was dismissed because of his temper and took the plans for Washington with him. Banneker recreated the plans from memory, saving the government the time and money of having to design the city.

Banneker took his study of astronomy seriously and was soon predicting future solar and lunar eclipses. He compiled the ephemeris, or information table, for annual almanacs that were published from 1792 through 1797. "Benjamin Banneker's Almanac" was a top seller from Pennsylvania to Virginia and even into Kentucky. The almanac also brought Banneker fame in England and France.

Slavery was a major issue throughout the life of Banneker. Even though he was never a slave himself, Banneker was concerned for all that had to live under such a deplorable system. These convictions on slavery cause him to write a letter to Thomas Jefferson, the author of the Declaration of Independence who wrote all men are created equal. It was this belief that Banneker questioned Jefferson about. Jefferson, who owned slaves on his Monticello plantation, was seen as a hypocrite by Banneker. In response to Banneker's letter, Jefferson politely stated, "such proofs as you exhibit...talents equal to those of the other colors of men," but he failed to comment on the political issues Banneker addressed in his letter. Jefferson also did not comment on a copy of Banneker's almanac.

Throughout his life, Banneker earned the respect of those that had prejudice beliefs towards African Americans. His intellectual brilliance and the color of skin, Banneker became internationally known as the "Sable Genius." He died quietly at his home in Ellicott Mills, Maryland in 1806. In honor of his contributions to the city of Washington, DC, a memorial circle and fountain have been constructed in the nation's capital. As a tribute to his quest for equal rights, the United States Postal Service issued a Benjamin Banneker stamp in 1980.