He functioned as head of the Department of Agitation and Propaganda in the Borsod-Abaúj-Zemplén County branch of the Hungarian Working People's Party (MDP) from 1954.

As the country was facing economic troubles and growing discontent, the aging party leader János Kádár decided to resign, although originally he had planned to remain in office until 1990.

Grósz remained prime minister until 24 November 1988, when he was succeeded by Miklós Németh, a representative of the radical reformer faction.

As 1989 wore on, Grósz was increasingly sidelined by the radical reformers within the party, including Németh, Rezső Nyers, Gyula Horn and Imre Pozsgay.

He tried to slow down, stop or reverse the radical changes advocated by his adversaries that were aimed at establishing a liberal political system and market economy in Hungary.

[1] Grósz's fate was sealed when he agreed to meet with Romanian leader Nicolae Ceaușescu to discuss what to do with a large number of ethnic Hungarians who had fled Romania.

Although Grósz retained his post as general secretary, Nyers now outranked him–and thus replaced him as the de facto leader of Hungary.