This thesis theorises and analyses the ways in which diasporas oppose authoritarian regimes from afar. Transcending the traditional debate about diasporas as radical or pacifying actors, and understanding diaspora politics as part of a broader opposition movement, it seeks to explain the conditions under which different configurations of relations between opponents at home and abroad prevail and the modalities of opposition associated to each configuration. Building on literatures that analyse diaspora politics from a social movement perspective, this thesis suggests that we can observe different forms of ‘opposition politics from afar.’ These two types of mobilisations are often combined but one or the other tends to prevail when diaspora activists at large act either as auxiliary forces subordinated to the opposition at home or as autonomous actors with their own political agenda. To understand these variations, the thesis argues that one must primarily look at the opposition dynamics at home, rather than at intrinsic characteristics of diaspora members, or at their relations with the host-country political environment only. Building its theoretical framework from an in-depth study of the Sri Lankan Tamil diaspora, including extensive interviews, the thesis argues that diasporic actors who are subordinated to or autonomous from homeland actors engage in two fundamentally different models of opposition politics from afar. More specifically, it shows that the political mobilisations of the Sri Lankan Tamil diaspora during the war (1983-2009) and in the postconflict period (since 2009) are respectively representative of models of ‘supportive politics’ and ‘exile politics’. During the war, Tamil political actors abroad were largely subordinated to the armed movement operating in Sri Lanka, the Liberation Tigers of Tamil Eelam (LTTE), which exerted its domination over the diasporic political field. Tamil migrants were ascribed an auxiliary role in which their primary task was to financially support the LTTE insurgency. After the LTTE’s defeat in 2009, the Tamil diaspora continued to fiercely oppose the Sri Lankan authorities from afar, but through entirely different modalities, this time representative of a model of exile diaspora politics. Tamil opposition forces abroad operated as autonomous actors, with their own political agenda, and prioritised the international arena as a site to conduct the nationalist struggle. Their practices consisted in attempts to convince international actors to take measures against the Sri Lankan government and in the promotion of the Tamil cause in its “pure” and “authentic” form abroad. Despite exhibiting different modalities, both types of exile diaspora politics were, unlike Tamil mobilisations during the war, strongly grounded in the political environment of migrants’ host-country and conductive to a broader ‘political integration’ of migrants in their country of settlement. The insights from the Tamil case are further developed through probing analysis of four additional cases of diaspora opposition politics. This examination reveals that the models of supportive and exile politics seem to prevail in other cases that display patterns of homeland opposition similar – though sometimes more hybrid – to either the period of the civil war or the post-conflict phase in Sri Lanka. Overall, the findings of the thesis contribute to the theoretical literature on diaspora politics, by tracing the process of how diaspora politics changes over time with the defeat or weakening of an armed organisation. by challenging approaches that focus on the social profile of diaspora members to explain their radical or pacifying attitudes and by going beyond analyses that understand diaspora politics primarily in relation to the context of the country of settlement. They also enhance our empirical knowledge about the fundamental differences between Tamil supportive politics during the war and Tamil exile politics in the post-war period