Best Marathon in Wales — Flat PB, Mountain or Coast

It depends on your goal. For a personal best, Newport is the clear pick, a fast road loop along the River Usk designed by double Olympian Steve Brace and billed as one of the flattest courses in Europe, with only about 26m of climb and a roughly 70% PB rate. For a true challenge, the Snowdonia Marathon Eryri circles Yr Wyddfa (Snowdon) and is regarded as one of the UK's toughest. For coastal scenery, the closed-road Tenby race in Pembrokeshire and the cliff-top Gower trail are hard to beat.

The Newport Wales Marathon is the flattest, with only around 26m of total elevation gain over the 26.2 miles, which the organisers bill as one of the flattest courses in Europe and Runner's World has listed among the fastest in the world. About 70% of finishers set a personal best there. The Great Welsh Marathon in Carmarthenshire is also long marketed as one of the flattest and fastest in the UK and is aimed at first-timers and PB chasers, though its 2027 edition moves to a brand-new venue confirmed closer to race day.

Very hard. The Snowdonia Marathon Eryri is widely called the toughest road marathon in the UK, a closed-road loop around Yr Wyddfa (Snowdon) from Llanberis with roughly 840m of total climb across three big ascents, including a punishing late climb at Waunfawr, and finishing on a steep, rough off-road descent. The total climb makes it a flat-equivalent of around 29 miles, so it is a challenge to be respected rather than a course for chasing a time. Check the gradients with our Elevation Profile tool. It routinely sells out, so enter through its ballot well in advance.

They sit at opposite ends of the spectrum, so the choice is really about your goal. Run Newport (a flat April road race along the River Usk) if you want a fast, achievable time and a high chance of a personal best. Choose Snowdonia (a hilly October mountain loop around Yr Wyddfa, with a slate finisher's medal) if the experience and the challenge matter more than the clock. Many Welsh runners do both in the same year, using Newport for the time and Snowdonia for the adventure.

Stick to the flat road races. Newport is the strongest PB course in Wales thanks to its 26m of climb and roughly 70% PB rate, and the coastal Great Welsh is similarly built for fast times. Avoid the hilly options if the clock is your priority: the closed-road Tenby coastal route has named climbs and around 330m of ascent, while the off-road Gower is over standard distance at roughly 44km (about 27.4 miles) with about 1,044m of climb, so both will run well outside your flat-road time. Model the gap with our Race Time Predictor.

Newport is the biggest standalone road marathon in Wales, with a field of around 4,000 and a wider festival of about 10,500 across the marathon, half, 10K and junior races. Wales's largest mass-participation running event overall is the Cardiff Half Marathon, with roughly 27,500 runners, but that is a half marathon rather than a full one, and Cardiff does not currently stage a standalone full marathon. For a big-city full marathon feel in Wales, Newport is the one.

Welsh marathons run from spring to late autumn. Newport opens the year in April in South Wales, followed by the closed-road Tenby race (the finale of Pembrokeshire's Long Course Weekend, with its famous red-carpet finish) in late June. The autumn cluster brings the flat Great Welsh in mid-October, the Snowdonia Marathon Eryri in North Wales in late October and the tough Gower coastal trail in early November, giving you a fast spring option and a scenic autumn run-up.