Phil Sesemann, 29, had never run a marathon before and only decided to enter the London race 15 weeks ago.
The Leeds City Athletics Club member is already a successful long-distance track athlete - but fell ill before his tilt at the 10,000 metres at the British Championships and decided in June to focus on the London Marathon instead.
He finished the elite men's race in seventh place with a time of 2:12:58 - narrowly outside the World Championships qualifying time of 2:11:30.
Sesemann also celebrated his 29th birthday today - and got a huge cheer from supporters along the Mall.
The University of Leeds graduate, who moved to the city as a student to read medicine, is a junior doctor at St James's Hospital.
He trains with Olympic 800-metre runner Alexandra Bell on the Leeds track and spent lockdown running on the Meanwood Valley Trail with his dog.
This year he was a late entry to the 3,000 metres at the European Indoor Championships and represented GB for the first time at a track event after Northallerton athlete Marc Scott withdrew. He had initially failed to qualify at the British trials.
Sesemann was a swimmer as a child and tried triathlon at university, but didn't take to cycling.
“I think swimming helps at an earlier age developing that aerobic base,” he said.
“I didn’t like the cycling. But again, the aerobic training from the triathlon saw my running improve and I just thought this is what I want to do and I’ve been all in on the running since 2013.”
He fits running around his shifts as part of the psychiatric team at the hospital, which can sometimes include three 12-hour night shifts in a row.
Through it all running was a hobby, first with a group of like-minded students, and then with Leeds City Athletics Club in 2018, when the combination of structured competition and the social aspect of it saw his performances improve.
“Leeds City has been great. In 2019 we had a really successful year and it provided me with a good balance of trying to perform at a high level on the national scene and also enjoying sport, spending time with my training partners.
“When you’re coming towards your late 20s, that keeps people in sport.”
Representative honours with Great Britain in cross-country events alongside Alexandra Bell followed, and even in lockdown he was able to keep running, even if his training partner was a little unorthodox.
“I’m lucky to live half a mile off the Meanwood Valley Trail so I was able to train on there with my dog, Kipchoge,” he laughs.
“I was quite fortunate that even in lockdown when you couldn’t train with anybody else, I could still exercise with her. It did wonders for my motivation, getting out with the dog on the trails every day. It was one of the simple pleasures.
“Being on the team I’ve already learned how single-minded the other athletes are. They’ll happily leave family, leave pets, leave homes just to go on training camps for months on end, whereas that’s something I’ve not been keen to do. Maybe that’s something I need to consider if I really want the top performances.
“For the next few years running could be the focus. I might be doing medicine til I’m 70, so I might as well enjoy it.”