The soldier, who cannot be identified for security reasons, had been drinking a coffee at the Westgate mall in Nairobi when militants stormed it on Saturday.
Despite the gunfire, he reportedly went back up to 12 times, helping people escape from the complex.
A witness told a UK newspaper:
‘What he did was so heroic. He was having coffee with friends when it happened.
‘He went back in 12 times and saved 100 people. Imagine going back in when you knew what was going on inside.’
A picture shows him helping two women out of the mall, a gun visible in his belt.
Following the 4 day siege, Kenya said their security forces were in full control, having done a sweep of the mall to rescue the final hostages.
‘Our forces are combing the mall floor by floor looking for anyone left behind. We believe all hostages have been released,' the Ministry of Interior said on Twitter early on Tuesday, confirming that his forces were 'in control 'of the building.
Kenya’s foreign minister Amina Mohamed, said today that a British woman extremist and ‘two or three’ Americans were among the terrorists behind the attack.
‘From the information that we have, two or three Americans (were involved) and I think, so far, I have heard of one Brit... a woman ... and I think she has done this many times before,’ she confirmed.
The death toll has risen to around 70- 6 of which are said to be Britons.
Philip Hammond, the Defence Secretary, warned the death toll could be even higher.
‘It is possible we will discover further British nationals once the building is fully secure,’ he said.