The performance of graphene-based transistors is often limited by the large electrical resistance across the metal-graphene contact. We report an approach to achieve ultralow resistance metal contacts to graphene transistors. Through a process of metal-catalyzed etching in hydrogen, multiple nanosized pits with zigzag edges are created in the graphene portions under source/drain metal contacts while the graphene channel remains intact. The porous graphene source/drain portions with pure zigzag-termination form strong chemical bonds with the deposited nickel metallization without the need for further annealing. This facile contact treatment prior to electrode metallization results in contact resistance as low as 100 Ω·μm in single-layer graphene field-effect transistors, and 11 Ω·μm in bilayer graphene transistors. Besides 96% reduction in contact resistance, the contact-treated graphene transistors exhibit 1.5-fold improvement in mobility. More importantly, the metal-catalyzed etching contact treatment is compatible with complementary metal-oxide-semiconductor (CMOS) fabrication processes, and holds great promise to meet the contact performance required for the integration of graphene in future integrated circuits.