The lightning bolt, extended a total of 477.2 miles (768 km) and spread across Mississippi, Louisiana, and Texas.
The previous record was 440.6 miles (709 km) and recorded in Brazil in 2018.
Lightning rarely extends over 10 miles and usually lasts under a second.
Another lightning flash recorded in 2020 - in Uruguay and Argentina - has also set a new record for duration at 17.1 seconds. The previous record was 16.7 seconds.