Mapam was formed by a January 1948 merger of the kibbutz-based Hashomer Hatzair Workers Party and the left-Labor Zionist Ahdut HaAvoda Poale Zion Movement.

In the elections for the first Knesset, Mapam received 19 seats, making it the second-largest party after the mainstream Labor Zionist Mapai.

From Mapam's point of view, the most important event of the second Knesset was the 1953 Prague Trials, which severely shook the party's faith in the Soviet Union.

The show trials, in which mostly Jewish leaders of the Communist Party of Czechoslovakia were purged, falsely implicated Mapam's envoy in Prague, Mordechai Oren, as part of a Zionist conspiracy.

After the Prague Trials and later, Nikita Khrushchev's Secret Speech at the 20th Party Congress in the Soviet Union, Mapam moved away from some of its more radical left-wing positions and toward social democracy.

The party then remained part of the Alignment until after the 1984 elections, when it broke away due to anger over Shimon Peres's decision to form a national unity government with Likud, taking six seats with it (later reduced to five when Muhammed Wattad defected to Hadash).

As a result of its declining support, Mapam joined with Ratz and Shinui to form Meretz, a new left-wing, social-democratic and pro-peace alliance, which became the third-largest party in the Knesset in the 1992 elections.

Mapam's executive committee advocated Jewish–Arab coexistence, opposed the expulsion of civilians and was in favor of the right of refugees to return to their homes after the war.

As a compromise Mapam agreed on condition that there was sufficient "surplus land" at each location to allow for the original inhabitants' return.

[13] The gulf between policy makers in the executive and Mapam members who dominated the leadership of the armed forces was again revealed following the military operations in the autumn of 1948.

In early November the editor of the Mapam newspaper, Eliezer Pra'i, received a letter describing events at al-Dawayima.

There followed a meeting of the Political Committee, 11 November 1948, which was briefed by recently ousted Chief of Staff of the Haganah, Yisrael Galili, about the killing of civilians during Operations Yoav and Hiram.