While scholarship on Arab nationalist mobilization in the 20th century has demonstrated openness to bottom-up approaches that center non-elite subjects, a predominant focus on statecraft remains in most of the literature on Pan-Arabism in the 1950s and 1960s. By contrast, this paper focuses on Palestinian grassroots mobilization to reframe Pan-Arabism’s decline as a contingent and relative phenomenon, exploring instead the intersections between the waning of secular, populist, and transnational Pan-Arabism and the emergence of new mobilizing projects centered on class and the nation-state. This paper examines the rise and fall of Pan-Arabist political organizing in Palestinian refugee camps in mid-20th century Jordan and Lebanon. To do so, the paper presents two social biographies of activists associated with the Arab Nationalists’ Movement (ANM), the organizational predecessor of the Popular Front for the Liberation of Palestine (PFLP) and the Democratic Front for the Liberation of Palestine (DFLP). These twin social biographies draw upon extensive archival research in periodicals and party pamphlets, published collections of ANM-linked documents and memoirs of former cadres, and interviews with former associates of the Movement, to examine how regional and global political shifts intersected with quotidian pressures of class, region, family ties, and social networks in the lives of Palestinian refugees. This grounding in oral testimonies enables the paper to compensate for some of the archival destruction that has restricted the study of Palestinian popular politics, allowing the paper to explore the changing dynamics of mid-20th century political organizing despite the limited accessible archival traces left by banned movements like the ANM. Both social biographies highlight the role of ANM-linked institutions such as presses, clubs, and youth groups in recruiting members and mobilizing allies between the MAN’s founding in 1951 and its 1970 dissolution. Not only did these institutions shape the political culture of Palestinian refugee camps: the paper argues that they enabled the Movement to transform into a grassroots political force by expanding its social bases. The paper also interrogates the ANM’s early turn to guerilla struggle and the growing fragmentation between the Movement’s Palestinian, Jordanian, and Lebanese networks, showcasing how even ideologically grounded activists’ political choices reflected the structuring influence of nation-state boundaries and subjectivities of class, gender, locality, and sect.