There has been a notable interest and growth in retrofitting of existing buildings due to its enormous potential in enhancing thermal comfort and energy efficiency. The increased interest in retrofitting has birthed several empirical studies within the research community. Notwithstanding, the various retrofitting techniques are yet to be synthesised to recognise the available retrofitting techniques that can promote sustainability in developing countries. Therefore, this study seeks to synthesise and gather various techniques in building retrofitting domains to achieve thermal comfort and energy efficiency in developing countries. A Scopus database publications search between 2002 and 2023 was carried out. An in-depth systematic review of building retrofitting was performed by assessing the output of thermal comfort and energy efficiency techniques. Also, a scientometric literature evaluation of selected articles is presented. VOSviewer is the software package used. The results showed that simulation techniques, deep machine learning, and field surveys are the dominant assessment techniques for building retrofitting. The result also shows that China, the United States, and Italy are the most contributed countries in the building retrofitting domain. Understanding the technique would help construction professionals’ decision-making in building retrofitting and stimulate innovative techniques for construction that improve building occupants’ thermal comfort and the performance of the building.