In the local (redshift z approximate to 0) Universe, collisional ring galaxies make up only similar to 0.01% of galaxies(1) and are formed by head-on galactic collisions that trigger radially propagating density waves(2-4). These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe(5-9). However, not much is known about distant (z > 0.1) collisional rings(10-14). 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(17-21). Contrary to previous predictions(10-12), 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.