The TV star and a team of helpers pieced together 20,000 sections of track over the original 2.75-mile Brooklands circuit near Weybridge in Surrey.The track, which opened in 1907 and closed in 1937, was the world's first purpose-built motorsport venue.
The team had to cross a river and roads to complete the circuit.
May was attempting the world record as part of his new television show, James May's Toy Stories.
It will now be scrutinised by Guinness World Records.
Once the track was finished, local residents and museum volunteers raced against a team of Scalextric Club members and enthusiasts.
The current record for a so-called slot car track measures 1.59 miles and was built in Berlin on 5 October 2007.
May has also created a house out Lego for the new series which sees him make life-size constructions out of toys.
James May - World Longest Scalextric - Longest slot car racing Video