Ben Grant, 30, has now spoken of the time he helped get his injured comrade to safety while mortars and artillery were fired at them in woodland north of Kharkiv earlier in May.
A helmet-mounted camera captured the rescue mission in dramatic footage.
Speaking about the incident now, the former Royal Marine - who is the son of Conservative MP Helen Grant - said he was focused on getting Grenadier Guardsman Dean Arthur out of danger.
He told The Daily Telegraph: “I was terrified, but driven to complete my most important goal, which at the time was getting him and my team out of the danger.”
“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.”
It comes as new footage emerged appearing to show volunteers in Ukraine - including Mr Grant - destroying a Russian tank with rocket launchers in an unverified clip.
Mr Grant said his foreign volunteer unit had been planning an assault on a Russian target before they were ambushed after being rumbled by drones.
It was then Mr Grant, an Afghanistan veteran who has been in Ukraine since March, said Mr Arthur knelt on a landmine “which had blown half of his leg off”.
Mr Grant could be heard shouting to his comrades in the footage: “We’ve got to move now or we’re gonna die.”
Footage showed the team carrying Mr Arthur before lying him down to tend to his wounds while they were under attack.
Mr Arthur, 42, from Stoke-on-Trent, Staffordshire, said he was “lucky” to be alive.
He added: “It was excruciating pain, with rounds incoming.”
Doctors saved Mr Arthur’s leg and now he remains in hospital in Kyiv where he said his injury has been “healing great”.
Father-of-three Ben Grant, a former Royal Marine, reportedly travelled to Ukraine in March.
Mr Grant held several junior ministerial roles under former Prime Minister David Cameron.
The Government has advised all Britons not to travel to Ukraine.
Defence Secretary Ben Wallace has warned British soldiers could be prosecuted for desertion if they head to Ukraine to fight against Russian forces.
In the Commons, he said: “The Ukrainians are very clear: you turn up, you are in it for the whole game. You are not in it for a selfie and six weeks, you are in it for real.
“I think we have seen already some people at the borders find that may be not be the right option to follow.”