Cognitive function during an ECT care pathway is mainly investigated at the group level by analyzing mean cognitive test scores over time. However, there are important inter-individual differences, with some patients experiencing residual invalidating cognitive deficits. This study provides a nuanced examination of cognitive functioning during and after ECT by combining three approaches for data analysis. A cognitive test battery was assessed in seventy-three ECT-treated patients with a Major Depressive Episode (MDE) at up to five time points (baseline, immediately prior to the third session and 1 week, 3 months and 6 months after completion of the index course). Group-level changes in cognitive function were investigated using linear mixed models and individual-level changes were examined using Reliable Change Indices (RCI). The presence of patient subgroups with similar cognitive trajectories was explored using Latent Class Growth Analysis (LCGA). At the group level, there was a temporary deterioration in processing speed, verbal memory and retrograde amnesia during and after index course of ECT. Individual-level analyses revealed considerable variability in cognitive effects of ECT. Three patient classes with a similar cognitive trajectory could be identified, all with a rather parallel courses over time, thus mainly differing in terms of pre-ECT cognitive functioning.