We present high cadence detections of two superflares from a bright G8 star ( V = 11.56 ) with the Next Generation Transit Survey ( NGTS ) . We improve upon previous superflare detections by resolving the flare rise and peak , allowing us to fit a solar flare inspired model without the need for arbitrary break points between rise and decay . Our data also enables us to identify substructure in the flares . From changing starspot modulation in the NGTS data we detect a stellar rotation period of 59 hours , along with evidence for differential rotation . We combine this rotation period with the observed ROSAT X-ray flux to determine that the star ’ s X-ray activity is saturated . We calculate the flare bolometric energies as 5.4 ^ { +0.8 } _ { -0.7 } \times 10 ^ { 34 } and 2.6 ^ { +0.4 } _ { -0.3 } \times 10 ^ { 34 } erg and compare our detections with G star superflares detected in the Kepler survey . We find our main flare to be one of the largest amplitude superflares detected from a bright G star . With energies more than 100 times greater than the Carrington event , our flare detections demonstrate the role that ground-based instruments such as NGTS can have in assessing the habitability of Earth-like exoplanets , particularly in the era of PLATO .