The MSZDP leadership entered into government as part of an unsuccessful post-war socialist administration and subsequently Béla Kun's Communist dictatorship, which carried out a Red Terror against those deemed to be enemies of the revolution and the working class.

The environment became increasingly hostile during the Second World War and activity virtually drained to a halt.

With the establishment of the police state, members were increasingly pressured to co-operate with the Hungarian Communist Party.

Under the leadership of Anna Kéthly, Gyula Kelemen and József Fischer the MSZDP took a prominent role in Imre Nagy's Provisional Government.

The MSZMP, now calling itself the Hungarian Socialist Party (MSZP), started with a large base of members, plenty of financial resources and a core electorate.

There were many disagreements throughout 1989 regarding the direction of the MSZDP, and a breakaway was established in November 1989 as the "Historical" Social Democratic Party (SZDP or tSZDP).

The results of the 1990 elections under the leadership of Anna Petrasovits was a huge disappointment to the MSZDP, as the reconstituted party failed to reach the 5% parliamentary threshold.

On its 45th Congress on 8 October 2011, Kapolyi was re-elected as chairman, and Andor Schmuck was elected as general secretary.

[6] At the 46th Congress on 24 November 2012, long serving chairman Kapolyi was not running again for re-election, Schmuck was elected as his successor.

The MSZDP did not participate in the 2018 general election and party leader László Hasilló endorsed Gergely Karácsony and his MSZP–Dialogue electoral alliance.

MSZDP also endorsed the candidacy of centre-right politician Péter Márki-Zay as prime minister of the united opposition.

After rejection, Cséplő announced MSZDP intends to take part in the 2022 parliamentary election with separate candidates and national list.

[1] However, the party's registration was refused by the National Election Office (NVI) due to for administrative reasons.

Party President László Kapolyi was elected MP and joined MSZP parliamentary group.