In recent years, there has been an increasing number of studies addressing older people's political participation. Much of this literature, however, can be criticised for neglecting important aspects of seniors’ political participation, such as its dynamics across the lifecourse, its gendered nature and the influence of the particular socio-political contexts in which participation occurs. In this paper we bring together all these issues to explore the relation between lifecourse transitions and participation in political organisations in Spanish men and women. We conducted life-story interviews with 40 highly engaged older political activists regarding their lifetime story of political commitment, and identified eight different lifecourse transitions affecting their participation in political organisations. Three of these transitions were related to the work domain and five to the family domain. Most of them were clearly gender-dependent, affecting men's and women's engagement in political organisations in different ways and to different degrees. Our study expands on previous research on lifespan-related aspects of political participation by showing that considering biographical, gendered and historical aspects is key to understanding the relationships between life transitions and participation in political organisations across the lifecourse.