Arnott was part of the England team competing in the inaugural Nitro Athletics Series events in Melbourne, Australia.
He took fourth in the men’s para ambulatory 100m race in a time of 11.25 seconds.
New Zealand’s Will O’Neil won in 10.68 seconds, with Australians Scott Reardon and Chad Perris second and third.
Arnott was part of the 24-strong England team, made up of 12 men and 12 women and captained by Christine Ohuruogu, who took part in the competition against Australia, New Zealand, China, Japan and Usain Bolt’s All Stars. The event will be shown on BBC2 on Sunday afternoon.
Meanwhile, fellow Plymouth international athlete Weir finished fourth for the University of Birmingham in a strong women’s race at the BUCS Cross Country Championships at Sheffield.
Brunel’s international Rebecca Murray won in 25.14 minutes, with St Mary’s Emily Hosker-Thornhill second in 25.32 and Loughborough’s Jessica Judd third in 25.43.
Weir, who clocked 26.16, was the first fresher home in the race.