Because as someone who's experienced the freefall of drugs and alcohol, everyday is a challenge.

Mulholland, a member of Rob de Castella's Indigenous Marathon Project, completed the 50-kilometre event at the Stromlo Running Festival in 6 hours, 38 minutes on Saturday.

He ran alongside Alex Lee, chief executive of The Glen - a rehabilitation centre on the Central Coast that Mulholland attended as a client and now works for.

It's those in recovery who the St Marys-native runs for, showing them what's possible on the other side of sobriety.

"It's a bit daunting [the ultramarathon] but like they say, this is where growth comes. Make it as uncomfortable as you can, if I can get through this I can get through a lot more," Mulholland said.

"I'll carry the IMF, my family and The Glen with [me for] every run forever now."

The 50-kilometre feat comes just three weeks after Mulholland completed his first marathon under the stars in Alice Springs.

Members of this year's IMP were meant to compete in the New York Marathon before it was canceled due to COVID-19, forcing de Castella and his team to relocate the finish line to Arrernte country.

Twelve athletes ran the midnight marathon and some met for the first time in person, having spent the last six months training remotely and doing the educational component online.

"It was hard not seeing everyone but it made it that much more special when we met in Alice," he said.

"I'm pretty easy going and can adapt to most things, so for me it wasn't a struggle. I got to be part of the year with the pandemic and still got a marathon done, in the middle of Alice Springs. I look at it that way.

"It wasn't about New York for me. I actually wanted to run a marathon in Alice before Covid hit. I'd rather do it there. Got my way, didn't I?"

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Mulholland crossed Simpson's Gap at 4:46:46. Although it was slower than what he would have liked, he was happy to pull through for his clients back at The Glen.

"It was a good experience because it was a full moon, midnight and in the middle of the desert. Not many people can say they've done that," Mulholland said.

"Towards the end it was hard, you hit that wall everyone talks about. The body wasn't holding up too well but I got through it.

"I was doing it for them - the clients back at The Glen - they got me across the line. I've been through some stuff myself, if I could get through that then I could get through this.

"As soon as I got back, it was high fives all day and people asking about the race. I think I got how my race went to them about 50 times in one day, so I pretty much spent a shift telling them what it was like and showing them photos of the midnight marathon."

Mulholland wants to establish a Fun Run on the Central Coast and an event in Mt. Druitt to help promote indigenous health following the IMP.

Having completed a marathon and 50-kilometre race, he also hopes to follow in the footsteps of IMP graduate Matt Heath and push towards a 100-kilometre event.

"I've grown hugely. It's given more more confidence that I can complete anything I put my mind to," Mulholland said.

"The marathon was pretty hard but now I've done it. Thrown in a 50-kilometre. Next year, who knows?

"I want to do something huge like Heath in a couple of years, to create noise and promote health for Aboriginal and Torres Strait Islander people."

The Stromlo Running Festival will continue with the 10-kilometre event on Sunday.