HONG KONG — A Hong Kong court sentenced dozens of leading pro-democracy figures to up to 10 years prison on Tuesday in the single largest trial under a national security law that critics say has been used to all but eliminate political dissent in the Chinese territory.

Benny Tai, 60, a former law professor at the University of Hong Kong who co-organized an unofficial primary election at the center of the case, was sentenced to 10 years in prison, the longest of the 45 sentences. The others…