“It’s against the Constitution to exclude artists from government support programs according to the taste of political power,” the presiding judge, Hwang Byeong-heon, said in his ruling.

Image Kim Jong-deok, a former culture minister, was sentenced to two years in prison. Credit... Ahn Young-Joon/Associated Press

The blacklisting of artists was a key element in the corruption and abuse-of-power scandal that led to Ms. Park’s impeachment in December and in the Constitutional Court ruling that officially removed her from office in March. Ms. Park, who was also arrested in March, is being tried separately on a string of criminal charges, among them collecting bribes from major businesses including Samsung and conspiring with her aides to discriminate against artists considered hostile to her government.

Revelations about the blacklist have infuriated the public, fueling widespread accusations that Ms. Park was taking South Korea back to the time when her father, the military dictator Park Chung-hee, ruled by gagging dissidents. For months, protesters gathered in huge weekend rallies in center of the capital, Seoul, demanding Ms. Park’s removal.

Judge Hwang said the discrimination against those on the blacklist was enforced “secretly, but persistently.”

He said the tactic had “humiliated” many Culture Ministry officials who were forced to implement it. Ms. Park conspired with Kim Jong-deok, the former culture minister, he said, to pressure into retirement a senior ministry official who did not cooperate with her policy.