The second VIIRS instrument was launched on-board the NOAA-20 (formerly JPSS-1) satellite on November 18, 2017. It was designed and built with the same performance requirements as the first VIIRS on-board the S-NPP launched on October 28, 2011. Currently, the NOAA-20 is orbiting the Earth in the same plane as the S-NPP but separated in time and space by 50 minutes. The VIIRS observations are made in 22 spectral bands, including a day-night band (DNB) that cover wavelengths from visible to long-wave infrared. The sensor’s on-orbit calibration is provided by a set of on-board calibrators (OBCs), which include a solar diffuser (SD), a solar diffuser stability monitor (SDSM), and a blackbody (BB). After turn-on, the VIIRS instrument conducted a series of post-launch testing (PLT) and intensive calibration and validation (ICV) activities, including those performed via spacecraft maneuvers, designed to verify and establish instrument on-orbit calibration performance baseline. This paper provides an overview of NOAA-20 VIIRS ICV activities and an assessment of its initial on-orbit performance with a focus on several key calibration parameters, such as the detector response (or gain), dynamic range, and signal-to-noise ratio (SNR). Various issues identified and lessons learned from initial instrument operation and calibration are also discussed in support of long-term monitoring (LTM) of NOAA-20 VIIRS calibration and data quality.