Ben Grant, 30, helped drag his comrade to safety as mortars and artillery were fired towards them in woodland north of Kharkiv earlier in May, with the rescue filmed on a helmet-mounted camera.
The former Royal Marine, who is the son of Conservative MP Helen Grant, said he was “terrified” but focused on getting former Grenadier Guardsman Dean Arthur out of danger.
He told The Daily Telegraph: “What was so scary was being so limited by trying to carry someone, when I can’t pull my weapon up, while there are attack helicopters overhead and tanks firing through the woods.
“It was unreal – I’ve never experienced anything like that in my life”.
He added: “Trying to do this [first aid] mid-firefight while there are Russians shooting over us and around us is just so difficult”.
Mr Grant, an Afghanistan veteran who has been in Ukraine since March, told the newspaper that his foreign volunteer unit had been gearing up for an assault on a Russian-held target when they were spotted by drones and ambushed.
Mr Arthur knelt on a landmine “which has blown half of his leg off”, Mr Grant said.
In the dramatic footage, Mr Grant can be heard shouting to his comrades: “We’ve got to move now or we’re gonna die.”
The team is seen carrying Mr Arthur through the undergrowth before lying him down to tend to his wound and tighten his tourniquet as bullets fly over their heads.
Mr Arthur, 42, from Stoke-on-Trent, Staffordshire, said: “It was excruciating pain, with rounds incoming”.
He added that he was “lucky” to have escaped alive.
“This type of camaraderie is only forged in these situations. If the coin was flipped, it was one of those guys, I would have got them out.”
Mr Arthur’s leg was saved by doctors, and he is in hospital in Kyiv where he said his injury is “healing great”.
The Government has advised all Britons not to travel to Ukraine and Defence Secretary Ben Wallace has warned British soldiers could be prosecuted for desertion if they head to Ukraine to fight against Russian forces.