The rapid pace of unattended urbanization has caused the urban heat island phenomenon, due to which the United Nations SDGs agenda 2030 calls for immediate actions for “sustainable cities and communities”. In this context, the case of the emerging metropolitan city Islamabad has been studied based on its developmental discourse vis-à-vis associated environmental problems. A time-series trend for the land surface temperature was generated by investigating the change in minimum and maximum variability against a dataset of 1960–2012 which was obtained from the Pakistan Meteorological Department, along with MODIS LST images from January 2000 to December 2015. The statistical comparison of an eight-day composite of the maximum (Tmax) and minimum (Tmin) temperature reveals an increasing trend with R2 values of 0.2507 (Tmin) and 0.1868 (Tmax). The box plots for both the Tmin and Tmax depict changes in seasonal patterns for Islamabad, with summers becoming longer and winters becoming harsher. Moreover, the application of the Mann–Kendall test affirmed the slope of the R2 linear trend map and showed the temperature regression in the Margalla Hills National Park and in such urban zones which had an expanded vegetative cover. These findings will act as a guide for urban planners and future researchers to maintain a standardized urban heat island and promote the concept of sustainable cities in the future course of action.