Yes
His beliefs were in line with Jeffersonian-Republicans, in the election of 1824 he was considered a Democratic-Republican, by the 1828 election he dropped Republican and became the first president of the Democratic party. Don't confuse his Democratic party with the modern Democratic party. The names/party is the same, but ideas on the role of government are different.
A Democratic-Republican, which was the political party that Jefferson co-created. It is also meant to describe someone in favor of a weak central government.
The question is backward: Jefferson's Democratic-Republican Party (formerly called the Anti-Federalists) split into the National Republican Party and the Democratic Party after the contested Presidential election of 1824.
Democratic-Republicans
James Madison and Thomas Jefferson started the Democratic-Republican party (but they just called it the Republican party). They created the Republican party to oppose the Federalist party. The Republican party that they created was the second political party in the United States.
The first organized party in America was made up of the followers of Jefferson, who, starting in the 1790s, called themselves Republicans (or Jeffersonian Democratic-Republicans). Hamilton and those who opposed Jefferson, kept the name Federalist. Jefferson's Republican Party has no ties to the current Republican Party. In fact, the current Democratic Party considerers Jefferson and Andrew Jackson as the founders of their party.
The modern Democratic Party wasn't formed until 1828, or 19 years after Meriwether's death by suicide. However, that party had historic roots back to 1792. While the main parties then were "Democratic-Republican" and "Federalist", President Thomas Jefferson was of the "Democratic-Republican" party. The modern Democratic Party came by a split of the "Democratic-Republican" party, and those who called themselves the Democrats were adhereing to Jeffersonian principles. All that is important as Meriwether Lewis was a political appointee of President Jefferson, so one may infer he was a Democrat. (However, the party's ideology has changed substantially in the two centuries since Meriwether's death.)
A third party
A third party
James Madison and Thomas Jefferson started the Democratic-Republican party (but they just called it the Republican party). They created the Republican party to oppose the Federalist party. The Republican party that they created was the second political party in the United States.
Thomas Jefferson created a party called the Democratic-Republican party, and his policies were somewhat different from the modern Republican Party.
Democratic-Republican Party was created in 1791.