The pair met Ukrainian President Volodymyr Zelensky on Sunday, a day after talks with Russian President Vladimir Putin in Moscow.
Their trip marked Witkoff and Kushner's first visit to Ukraine since Russia's full-scale invasion.
Their journey to Kyiv was complicated by Russian strikes on the city's airports on Saturday, forcing the envoys to travel by train from Moscow via Rzeszów in Poland rather than fly.
Zelensky described the talks as "very substantial", saying they covered security and economic guarantees for Ukraine, supplies of air-defence missiles and a support package for the winter.
He said he hoped three-way talks involving Ukraine, Russia and the US would resume soon.
Witkoff struck a similar tone, saying the US team had been "very encouraged" by what he called a "substantive, important" discussion.
Kushner told reporters he hoped talks would return to a trilateral format and that Washington was working to construct a "peace package".
Former Ukrainian Foreign Minister Dmytro Kuleba said the main achievement was simply that dialogue had resumed after months of deadlock.
But he cautioned that there was no sign that either Moscow or Washington had shifted its position, and no new proposals were on the table.
He described that as both a shortcoming and, in some ways, a relief, given that some previous ideas were "better off not existing."
Russia's territorial demands remain the main sticking point.
The Kremlin is seeking control of the whole of Donbas and other eastern Ukrainian regions, while Kyiv is pushing for a three-way summit involving the leaders of Ukraine, Russia and the US.
(ał)
Source: IAR, Reuters