Trust in individuals is strongly guided by group membership; ingroup favouritism in trust is a very robust finding in the literature on pro-social behaviour. We know, however, that group attitudes can change based on discrete encounters with group members (i.e., intergroup contact). This research examines how people use previous experiences with ingroup and outgroup members to inform decisions to trust novel, unknown group members. This process, which we refer to as member-to-member generalisation, was examined in two studies using a student sample (N = 135) and a larger and more representative online sample (N = 226). The moderating effects of group membership (ingroup vs outgroup vs unknown) and interaction valence (positive vs negative) on member-to-member generalisation were explored in ten sequential Trust Games. We examined changes in investment behaviour based on feedback from the previous partner, where feedback was either positive (high reciprocation) or negative (no reciprocation). We observed consistent evidence for member-to-member generalisation. People did not just rely on initial group attitudes to guide their trust behaviour, but adjusted their behaviour towards novel individuals based on previous experiences. Generalisation was stronger for interactions that were negative and seemingly unexpected. When people showed strong distrust of the outgroup (Study 1) or were highly identified with the ingroup (Study 2), they changed their behaviour towards novel partners more after experiencing incongruent interactions. These findings are discussed in relation to intergroup contact theory, outgroup homogeneity, and expectancy violation effects.