After graduation, he served in the 58th Combined Arms Army as the commander of a separate tank battalion.

[citation needed] In 2020, he graduated from the faculty of retraining and advanced training of the highest command personnel of the Military Academy of the General Staff.

[3][9] In late March, he visited the front line and awarded a medal to his son, the commander fighting in Sumy and Chernihiv, just before the Russian army withdrew.

[10] An investigation by NPR alleged that troops under Lapin's command had killed civilians in Nova Basan and Bobrovytsia during the first months of the invasion and suggested that Lapin could be prosecuted for war crimes under the doctrine of command responsibility if the killings were sufficiently widespread.

[11] Following the October 2022 recapture of Lyman by Ukrainian forces, Lapin was heavily criticized by the head of the Chechen Republic, Ramzan Kadyrov.

[12] On October 29 Lapin was dismissed as commander from the Central Military District,[13] replaced by Alexander Linkov.

[15] In the months leading up to the August 2024 Ukrainian incursion into Kursk, Lapin dismantled a border guard council that had been responsible for its protection.

Colonel Denis Aleksandrovich Lapin, commanding officer of the 1st Guards Tank Regiment v/ch 58198.