In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies¹ and are formed by head-on galactic collisions that trigger radially propagating density waves^2,3,4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe^5,6,7,8,9. However, not much is known about distant (z 0.1) collisional rings^{10,11,12,13,14}. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, diffuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved^15,16, the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals^{17,18,19,20,21}. Contrary to previous predictions^10,11,12, this work suggests that massive collisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.