This study aimed to examine the effects of crude garden cress seed oil (CGCSO) on frozen–thawed boar sperm qualities. Semen ejaculates (n = 12) were collected and further divided into six equal aliquots based on CGCSO concentrations (0, 0.5, 1, 1.5, 2, and 2.5% v/v) in the freezing extender. Semen samples were processed and cryopreserved utilizing the traditional liquid nitrogen vapor technique. Subsequently, semen samples were thawed in a thermos with warm water at 50 °C for 12 s and evaluated for sperm morphology using scanning electron microscopy, sperm motility using a CASA, sperm viability, acrosome integrity, mitochondrial function, MDA level, total antioxidant capacity (TAC), glutathione peroxidase (GSH-Px), and catalase (CAT) activity. The results indicated that 1% CGCSO resulted in superior post-thaw sperm characteristics, including enhanced sperm morphology, motility, viability, acrosome integrity, and mitochondrial function. Particularly, the total motile sperm increased by 16.5%, progressive motile sperm increased by 13.0%, viability improved by 15.1%, acrosome integrity increased by 14%, and mitochondrial function improved by 14.1% compared to the control group. CGCSO treatment at 1% and 1.5% exhibited the lowest level of MDA (45.73 ± 11.2 and 45.73 ± 11.3 µmol/L, respectively) compared to the other groups. The CGCSO-supplemented groups showed higher values of TAC, GSH-Px, and CAT than the control group but not significantly.