Immune checkpoint inhibitor-associated diabetes mellitus (ICI-DM) is a rare immune-related adverse event and is usually considered permanent. Here, we report the first case of a 54-year-old man with ICI-DM who recovered from insulin dependence. He was diagnosed with lung cancer and started pembrolizumab therapy. After seven cycles, he developed ICI-associated secondary adrenal insufficiency and started hydrocortisone supplementation. Subsequently, he complained of fatigue, and blood examinations showed hyperglycemia with ketosis. A glucagon challenge test indicated insulin dependence. He was diagnosed with ICI-DM and insulin therapy was initiated. Pembrolizumab therapy was discontinued due to concomitant ICI-associated hepatitis. Six months later, a glucagon challenge test result showed an improvement in insulin secretion, and insulin therapy was discontinued. The lung cancer lesions continued to shrink. Even if ICI-DM develops, it might be possible to control the underlying cancer while avoiding lifelong insulin therapy through early discontinuation of ICI.