New York City has emerged as the global epicenter for the coronavirus disease 2019 (COVID-19) pandemic. The city's public health system, New York City Health + Hospitals, has been key to the city's response because its vulnerable patient population is disproportionately affected by the disease. As the number of cases rose in the city, NYC Health + Hospitals carried out plans to greatly expand critical care capacity. Primary intensive care unit (ICU) spaces were identified and upgraded as needed, and new ICU spaces were created in emergency departments, procedural areas, and other inpatient units. Patients were transferred between hospitals to reduce strain. Critical care staffing was supplemented by temporary recruits, volunteers, and Department of Defense medical personnel. Supplies needed to deliver critical care were monitored closely and replenished to prevent interruptions. An emergency department action team was formed to ensure that the experience of front-line providers was informing network-level decisions. The steps taken by NYC Health + Hospitals greatly expanded its capacity to provide critical care during an unprecedented surge of COVID-19 cases in NYC. These steps, along with lessons learned, could inform preparations for other health systems during a primary or secondary surge of cases.