The Prime Minister met the Ukrainian President on Saturday in a surprise visit to the war-torn capital.
A video has now emerged revealing how Mr Johnson conducted the high-risk visit.
In the clip, the PM reiterates that the British people “stand in sympathy and in solidarity” with the Ukrainians as he travels on a train from Poland to Kyiv.
During his eventual meeting with Mr Zelenksy following the train journey, Mr Johnson hailed the fightback against Russian forces as the “greatest feat of arms” this century.
After the talks, Downing Street vowed Britain would send 120 armoured vehicles and new anti-ship missile systems to Ukraine as part of a package of £100million in military aid.
Speaking after the meeting, Mr Johnson said: “Ukraine has defied the odds and pushed back Russian forces from the gates of Kyiv, achieving the greatest feat of arms of the 21st century.
“It is because of President Zelensky’s resolute leadership and the invincible heroism and courage of the Ukrainian people that Putin’s monstrous aims are being thwarted.
“I made clear today that the United Kingdom stands unwaveringly with them in this ongoing fight, and we are in it for the long run.
“We are stepping up our own military and economic support and convening a global alliance to bring this tragedy to an end, and ensure Ukraine survives and thrives as a free and sovereign nation.”
President Volodymyr Zelensky’s chief diplomatic adviser said Mr Johnson’s visit was “very timely and very important in terms of war”.
Igor Zhovkva told Sunday Morning on BBC One that the visit came at the invitation of Mr Zelensky.
He told the programme: “Any visit that is happening now to the Ukraine is done on the invitation of the president of the Ukraine. Prime Minister Johnson received this invitation and he agreed. It might be a surprise for you but it is not a surprise for us. We were preparing for a while. This visit was very timely and very important in terms of war.”
Mr Zhovkva described Mr Johnson as being “very supportive” during previous discussions before the war began about “the potential danger which Russian aggression might have”.
Mr Zhovkva said many leaders are coming to Kyiv to show support – but he said they must come “not only with their show of support but something that will have meaning, which has results”.
He said Mr Johnson’s talks were productive because he “did not come empty-handed” and the leaders discussed important issues such as military and financial support in addition to “rebuilding Ukraine when we will win”.