Background: Very preterm (<32 weeks’ gestational age; VP) or very low–birth weight (<1,500 g; VLBW) birth has been associated with increased risk for anxiety and mood disorders and less partnering in adulthood. The aim was to test whether (a) VP/VLBW are at increased risk of any anxiety or mood disorders from 6 to 26 years compared with term-born individuals; (b) social support from romantic partners is associated with protection from anxiety and mood disorders; and (c) VP/VLBW adults’ lower social support mediates their risk for any anxiety and mood disorders. Methods: Data are from a prospective geographically defined longitudinal whole-population study in South Bavaria (Germany). Two hundred VP/VLBW and 197 term individuals were studied from birth to adulthood. Anxiety and mood disorders were assessed at 6, 8, and 26 years with standardized diagnostic interviews and social support via self-report at age 26. Results: At age 6, VP/VLBW children were not at increased risk of any anxiety or mood disorder. At age 8, VP/VLBW more often had any anxiety disorder than term comparisons (11.8% vs. 6.6%, OR = 2.10, 95% CI [1.08–4.10]). VP/VLBW adults had an increased risk for any mood (27.5% vs. 18.8%, OR = 1.65 [1.02–2.67]) but not for any anxiety disorder (33.0% vs. 28.4%, OR = 1.27 [0.82–1.96]). None of the significant differences survived correction for multiple testing. Social support was associated with a lower risk of anxiety or mood disorders in both groups (OR = 0.81 [0.68–0.96]) and mediated the association of VP/VLBW birth with any anxiety or any mood disorders at age 26. Conclusions: This study does not show a persistently increased risk for any anxiety or mood disorder after VP/VLBW birth. Low social support from a romantic partner mediates the risk for anxiety or mood disorders after VP/VLBW birth.