The aggregation of peptides on a lipid bilayer is studied using coarse-grained molecular dynamics in implicit solvent. Peptides bind to and self-assemble on the membrane surface into beta-rich fibrillar aggregates, even under conditions where only disordered oligomers form in bulk solution. Relative to a solid surface, the membrane surface facilitates peptide mobility and a more complex network of morphology transitions as aggregation proceeds. Additionally, final aggregate structures realized on the membrane surface are distinct from those observed on a comparable solid surface. The aggregated fibrils alter the local structure and material properties of the lipid bilayer in their immediate vicinity but have only a modest effect on the overall bending rigidity of the bilayer.