In this systematic review, we summarize the current understanding and controversies on cognitive sequelae after traumatic brain injury (TBI) to understand the cognitive deficits such as memory, attention, executive functions, and unawareness of their deficits in TBI patients. This review presents the cognitive sequel of patients with moderate-to-severe TBI by a comprehensive focused conglomeration of research publications by searching various resources. A search strategy with specific inclusion criteria was performed in PubMed, Cochrane, Web of Science, and the WHO Global Health Library. This review noted that TBI is related with increase of various neurological and non-neurological disorders including problems with attention, inability to concentrate, speech and language dysfunctions, learning and memory impairment, impaired reasoning, impaired planning and problem-solving. This review found that patients' cognitive deficits are common in victims of moderate to severe TBI often as the long-lasting sequalae. The present review suggests that there is a need for further research to develop unique rehabilitation methods that will help to enhance brain plasticity and process of recovery after TBI.