Despite the early inclement weather, the gruelling all-day event has proved hugely popular with spectators lining the banks of Waterloo Lake and the cycle and running routes.
The race began at 6am with swimmers taking to the lake for two loops totalling 2.4 miles.
From there they climbed out of the water onto their saddles for a leg-burning 112-mile three-loop court on their bikes, before running a strength-sapping four-loop spectator-friendly course over 26 miles - marathon length.
Still ongoing, it is expected to continue for up to 17 hours.
Ironman and triathlon events have seen a resurgence in recent years, particularly in West Yorkshire thanks to the home-grown success of Leeds-born brothers Alistair and Jonny Brownlee, who dominated the sportin the 2010s and picked up numerous Olympic medals and world championship titles.
And due to its predicted popularity, roads were closed all around Roundhay Park today to accommodate the route and the sheer volume of spectators.
14. Roundhay Ironman Competition
Running through transition for the cycling. | Steve Riding
15. Roundhay Ironman Competition
Ironman cyclists make their way along Wetherby Road. | Steve Riding
16. Roundhay Ironman Competition
Riders settle in for the cycling part of the competition. | Steve Riding
17. Roundhay Ironman Competition
Swimming completed, the competitors make their way to their bikes. | Steve Riding
