Sobotka was born in Telnice but soon moved with his family to Slavkov u Brna. He studied law at the Masaryk University in Brno and earned magister degree in 1995. After the fall of communism he helped rebuild Czech Social Democratic Party (ČSSD) and became a member. Sobotka also co-founded Young Social Democrats, youth wing of the ČSSD. He was first elected to the Chamber of Deputies in the 1996 legislative election.