Aortic dissection (AD) is a life-threatening vascular disease with limited treatment strategies. Here, we show that loss of the GWAS-identified SH2B3 gene, encoding lymphocyte adaptor protein LNK, markedly increases susceptibility to acute AD and rupture in response to angiotensin (Ang) II infusion. As early as day 3 following Ang II infusion, prior to the development of AD, Lnk–/–aortas display altered mechanical properties, increased elastin breaks, collagen thinning, enhanced neutrophil accumulation, and increased MMP-9 activity compared with WT mice. Adoptive transfer of Lnk–/–leukocytes into Rag1–/–mice induces AD and rupture in response to Ang II, demonstrating that LNK deficiency in hematopoietic cells plays a key role in this disease. Interestingly, treatment with doxycycline prevents the early accumulation of aortic neutrophils and significantly reduces the incidence of AD and rupture. PrediXcan analysis in a biobank of more than 23,000 individuals reveals that decreased expression of SH2B3 is significantly associated with increased frequency of AD-related phenotypes (odds ratio 0.81). Thus, we identified a role for LNK in the pathology of AD in experimental animals and humans and describe a new model that can be used to inform both inherited and acquired forms of this disease.