Veterans with serious mental illness (SMI) are at high risk of exacerbation of mental illness in pregnancy and postpartum, with consequences including poor pregnancy outcomes, decreased functioning, and impaired child development. Peer support could play a key role in supporting pregnant and postpartum Veterans with SMI. In this study, investigators will develop (Aims 1 and 2) and pilot (Aim 3) a peer specialist-delivered perinatal mental health intervention for Veterans with SMI, drawing from evidence-based models and input from Veterans, key VA clinical staff, and subject matter experts. The intervention will be piloted to assess its feasibility and acceptability, as well as exploratory clinical outcomes including postpartum functioning and mental health symptoms.