A cooling system and method are provided for facilitating cooling of multiple liquid-cooled electronics racks. The cooling system includes a main system coolant supply loop with a plurality of system coolant supply branch lines for facilitating supply of cooled system coolant to the electronics racks, and a main system coolant return loop with a plurality of system coolant return branch lines for facilitating return of exhausted system coolant from the electronics racks. When operational, cooled system coolant circulates through the coolant supply loop and exhausted system coolant circulates through the coolant return loop. A plurality of modular cooling units are coupled to the coolant supply loop and coolant return loop. Each modular cooling unit includes a heat exchanger to facilitate cooling of a portion of the exhausted coolant circulating through the main system coolant return loop for return as cooled system coolant to the main system coolant supply loop.