The Ministry of Defence (MoD) said they spoke during the previously unannounced trip about continuing to aid the resistance against Russia, “as the conflict enters a different phase”.
Officials would only say that the two-day visit took place “this week” and it was not known whether they discussed the Britons condemned to death for fighting Russian forces.
Ministers are under pressure to secure the release of Aiden Aslin, 28, and Shaun Pinner, 48, after the pair were told they will face a firing squad for acts of terrorism after a “show” trial by pro-Moscow officials in Russian-controlled east Ukraine. They were captured while fighting with the Ukrainian army in Mariupol.
A video on Mr Zelenskyy’s Telegram channel showed Mr Wallace tell the president “you’re doing amazing” during the visit.
The president replies: “We do it together.”
Mr Wallace, who also held discussions with his Ukrainian counterpart Oleksii Reznikov, wanted to hear “first-hand” how the army’s requirements are “developing as the nature of the conflict continues to change”.
“This will ensure that the UK’s continued support is evolving to meet those requirements and is tailored to the situation on the ground,” the MoD said.
“The three agreed to work even more closely going forward in support of their shared goal of enabling Ukraine to liberate itself from illegal Russian occupation.
“They also discussed the range of equipment and training the UK is currently providing and what further support we can offer to help Ukrainian forces to defend their country.”
Mr Zelenskyy presented him with what appeared to be a signed and framed collection of stamps. They bore a slogan containing an expletive that has become a symbol of the national resistance after a Ukrainian guard defending Snake Island in the Black Sea used colourful language to dismiss an attacking ship.