Karl Harald Wiik (13 April 1883 – 26 June 1946) was a Swedish-speaking Finnish Social Democratic (SDP) leader.

Imprisoned during the years of World War II, Wiik was released in 1944, becoming a leader of the Finnish People's Democratic League (SKDL), a left wing political organization dominated by the newly legalized Communist Party of Finland (SKP).

An influential member of the Party's left wing, he was imprisoned for a time after the Finnish Civil War for having participated in the revolutionary government.

[dubious – discuss] The six expelled MPs formed the short-lived Socialist Parliamentary Group, all of whose members spent the years 1941 to 1944 in prison because of their unrelenting opposition to the Continuation War.

Wiik, in contrast, wrote that "For me, Socialism is the most important thing; one must not sell it in order to win a few bourgeois votes.