Thomas Jefferson was a Founding Father, the main writer of the Declaration of Independence, the third U.S. president, and a key architect of early American government, education, and expansion.

What Did Thomas Jefferson Do?

Big Picture

  • Helped launch the United States as an independent nation.
  • Led the country as president from 1801–1809.
  • Expanded U.S. territory dramatically with the Louisiana Purchase.
  • Pushed ideas about religious freedom, public education, and republican government.

Founding Father and Thinker

  • Jefferson was born in Virginia in 1743 and became a lawyer, landowner, and political thinker deeply influenced by Enlightenment philosophy.
  • He was elected to the Continental Congress as tensions with Britain escalated and quickly became one of the key voices for independence.
  • In 1776, he served on the Committee of Five and was chosen as the principal author of the Declaration of Independence, drafting the text that announced the colonies’ break with Britain and laid out natural rights like “Life, Liberty, and the pursuit of Happiness.”

Jefferson’s Declaration turned revolutionary anger into a universal-sounding statement of human rights, which people still quote and argue about today.

Laws, Liberty, and Religion

After independence, Jefferson went to work reshaping laws in Virginia:

  • He helped revise state laws, drafting over 100 bills in a few years to modernize the legal system.
  • He pushed to abolish primogeniture and entail (rules that kept land and power in the hands of the eldest son), because he feared a hereditary aristocracy.
  • He wrote the Virginia Statute for Religious Freedom (enacted 1786), which:
    • Disestablished the Anglican Church as the official state religion.
    • Guaranteed religious liberty for Virginians.

Jefferson later had this statute listed on his tombstone as one of his three proudest achievements, alongside the Declaration of Independence and the founding of the University of Virginia.

President of the United States

Jefferson served as the third president from 1801 to 1809.

During his presidency, he:

  • Tried to shrink the federal government, cutting military spending and reducing its size and cost.
  • Focused on defending American trade and shipping, especially against Barbary pirates and aggressive British policies.
  • In 1803, approved the Louisiana Purchase from France:
    • Cost about 15 million dollars.
* Roughly doubled the land area of the United States, adding about 828,000 square miles from the Mississippi River to the Rocky Mountains.
  • Ordered the Lewis and Clark Expedition (1804–1806) to explore and map the new western territories and study the land, resources, and Native nations.
  • Responded to British and French interference with U.S. shipping during the Napoleonic Wars by signing the Embargo Act of 1807, which limited foreign trade to pressure them but caused serious economic pain at home.

Inventor, Architect, and Educator

Jefferson was also a curious experimenter and designer:

  • He designed and improved practical devices, including:
    • A steel plow.
    • A “polygraph” copying device (for duplicating letters).
    • A macaroni machine that helped popularize pasta and tomato dishes in America.
  • He was heavily involved in architecture, designing his home Monticello and other buildings in a neoclassical style.
  • In 1819 he founded the University of Virginia, carefully planning its curriculum and campus layout; he saw education as the foundation of a healthy republic.

Again, he considered founding the University of Virginia one of his top three accomplishments, important enough to engrave on his tombstone.

Legacy and Ongoing Discussion

Today, when people ask “what did Thomas Jefferson do,” they usually mean:

  • He authored the Declaration of Independence and helped define American ideas of rights and liberty.
  • He expanded the country westward with the Louisiana Purchase and backed the Lewis and Clark Expedition.
  • He promoted religious freedom and public education and founded a major public university.
  • He led the U.S. as its third president during a formative period in its history.

At the same time, modern discussions (including online forums and classroom debates) also focus on the contradictions of a man who championed liberty while owning enslaved people, and who wrote universal ideals that his society did not extend to everyone. Those tensions are a big part of why Jefferson remains a controversial and widely discussed figure today.

TL;DR: Thomas Jefferson helped create the United States on paper and in practice—writing the Declaration of Independence, serving as the third president, expanding the country with the Louisiana Purchase, and pushing for religious freedom and public education—while leaving a legacy that is influential, admired, and heavily debated.

Information gathered from public forums or data available on the internet and portrayed here.