No, both partners do not need to be self-employed when applying for a mortgage together. Lenders will assess the combined income and financial circumstances of both applicants. If one partner is employed and the other is self-employed, lenders will consider both income streams in their affordability assessment. The employed partner's stable income can sometimes offset the variability of self-employed income, potentially strengthening the overall application. However, both partners' credit histories and financial commitments will be taken into account.