This article operationalises Simondon’s theory of becoming and Deleuze and Spinoza’s ethics and unfolds their conceptualisations in the lives of a group of irregular migrants in Finland. From an ontological and ontogenetic perspective, individuals and their environment are always in a non-complete, non-linear and ethically affective state of becoming. In this sense, migrant bodies register the positive and negative affections accumulated over time, and, via information, make them a material, yet unfinished, and ready to be challenged again, part of their becoming. Applying these concepts to ethnographic fieldwork, this article highlights three dimensions of the observed irregular migrants’ becoming: their relentless efforts of becoming themselves through hardships; non-linear tensions with disparate realities, such as the bureaucratic procedures, and the negative affections the latter entail; and the struggle towards positive affections in temporary stabilities (e.g. in community life). In focusing on the processual and ontological making of migrants in their environment, the article contributes to broader debates regarding the non-linear and ethical dimensions of their everyday lives, as well as their capacity of transforming themselves, and aims at opening up dialogues on the significance of an ontogenetic approach to the field of irregular migration and beyond.