No, he was a democrat.
Joe Wilson, S. Carolina, Republican
Warren G. Harding was the first Republican President after World War I. He was inaugurated in 1921, after Woodrow Wilson's term ended.
In a way this is what happened in 1912. Former President Theodore Roosevelt, who was elected as a Republican Vice President in 1900 and as a Republican President in 1904, tried to get the nomination in 1912, but when he failed to get it, he ran as a third party candidate against the incumbent Republican president William Howard Taft. Both were defeated by Democrat Woodrow Wilson.
The Republican vote was divided between Taft and Roosevelt, which allowed Democrat Woodrow Wilson to win. Similar outcomes occurred in 1992 and 2000.
Theodore Roosevelt, former Republican president, ran against both Taft and Wilson in 1912 as a third party candidate. He and Taft added together won more votes that the winner, Wilson.
Theodore Roosevelt and William H. Taft divided the Republican vote, which allowed Wilson to be elected as a Democrat.
Republican
President Ford Was a Republican
Woodrow Wilson won the Electoral College with 435 votes, In 1912, former Republican president, Theodore Roosevelt failed to get the Republican nomination over the incumbent President Taft, so he formed his own "Bull Moose" party and ran anyway in opposition to Taft as well as the Democrat Wilson. Roosevelt split the Republican vote. Wilson won even though added together, Roosevelt and Taft got enough votes to win.
Of the three, Dr. Woodrow Wilson was the Democrat.
William Howard Taft was the incumbent Republican President and was nominated for a second term by his party in 1912. Teddy Roosevelt who started off as a Republican left and started a new party. This cost Taft the re-election and put a Democrat, Woodrow Wilson in as President.
Representative Joe Wilson, Republican of South Carolina