In the prelude to the invasion, he told Ukrainian President Volodymyr Zelenskyy that Russian troops would invade Ukraine from Belarus and through the Chernobyl exclusion zone, which was correct.

His troops had to retreat, and Russia partially occupied part of Luhansk Oblast in the subsequent years.

On June 13, 2019, Ukrainian President Volodymyr Zelenskyy appointed him to head of the SBGS, replacing Petro Tsyhikal.

The SBGS then "completely evacuated all secret documentation of personal and housing files of our staff" from multiple cities across the country, and prepared for a different Russian troop movement to surround Ukrainian soldiers currently fighting in Donetsk and Luhansk Oblasts.

[3] Despite Russian troops amassing in Crimea, Deineko did not believe Russia would invade from there, predicting it to be a false flag attack.

At 5:17, Deineko again notified Zelenskyy of the invasion via text:[3][7][9] Good morning, dear Mr President.

Head of the State Border Guard Service of Ukraine, Major General Sergey DeynekoAfter the invasion started, the SBGS fell under the Ukrainian Armed Forces' control.

[11] In July 2023, Zelenskyy held a meeting with Deineko and the rest of the president's Staff on the situation on the front lines, the security of nuclear power plants, and the pace of production of military equipment and ammunition.

[12] In December 2023, Deineko visited Kharkiv Oblast to inspect and discuss the positions of his troops on the front lines.