Loop-mediated isothermal amplification (LAMP) is a versatile technique for detection of target DNA and RNA, enabling rapid molecular diagnostic assays with minimal equipment. The global SARS-CoV-2 pandemic has presented an urgent need for new and better diagnostic methods, with colorimetric LAMP utilized in numerous studies for SARS-CoV-2 detection. However, the sensitivity of colorimetric LAMP in early reports has been below that of the standard RT-qPCR tests, and we sought to improve performance. Here we report the use of guanidine hydrochloride and combined primer sets to increase speed and sensitivity in colorimetric LAMP, bringing this simple method up to the standards of sophisticated techniques and enabling accurate, high-throughput diagnostics. This study describes enhancing loop-mediated isothermal amplification through the addition of guanidine chloride and the use of multiple primer sets for different gene targets combined in a single reaction. We demonstrate a five- to tenfold increase in sensitivity for colorimetric SARS-CoV-2 detection, further improved by use of absorbance measurement using a standard plate reader format. These alterations to the simple and rapid colorimetric loop-mediated isothermal amplification method increase performance and can be used as the basis for sensitive isothermal molecular diagnostic tests.