We report the discovery of NGTS-2b , an inflated hot-Jupiter transiting a bright F5V star ( 2MASS J14202949-3112074 ; T _ { eff } = 6478 ^ { +94 } _ { -89 } K ) , discovered as part of the Next Generation Transit Survey ( NGTS ) . The planet is in a P= 4.51 day orbit with mass 0.74 ^ { +0.13 } _ { -0.12 } M _ { J } , radius 1.595 ^ { +0.047 } _ { -0.045 } R _ { J } and density 0.226 ^ { +0.040 } _ { -0.038 } g cm ^ { -3 } ; therefore one of the lowest density exoplanets currently known . With a relatively deep 1.0 \% transit around a bright V= 10.96 host star , NGTS-2b is a prime target for probing giant planet composition via atmospheric transmission spectroscopy . The rapid rotation ( v sin i = 15.2 \pm 0.8 km s ^ { -1 } ) also makes this system an excellent candidate for Rossiter-McLaughlin follow-up observations , to measure the sky-projected stellar obliquity . NGTS-2b was confirmed without the need for follow-up photometry , due to the high precision of the NGTS photometry .