The promotion of global sustainability within environmental science courses requires a paradigm switch from knowledge-based teaching to teaching that stimulates higher-order cognitive skills. Non-major undergraduate science courses, such as environmental science, promote critical thinking in students in order to improve the uptake of scientific information and develop the rational decision making used to make more informed decisions. Science, engineering, technology and mathematics (STEM) courses rely extensively on visuals in lectures, readings and homework to improve knowledge. However, undergraduate students do not automatically acquire visual literacy and a lack of intervention from instructors could be limiting academic success. In this study, a visual literacy intervention was developed and tested in the face-to-face (FTF) and online sections of an undergraduate non-major Introduction to Environmental Science course. The intervention was designed to test and improve visual literacy at three levels: (1) elementary—identifying values; (2) intermediate—identifying trends; and (3) advanced—using the data to make projections or conclusions. Students demonstrated a significant difference in their ability to answer elementary and advanced visual literacy questions in both course sections in the pre-test and post-test. Students in the face-to-face course had significantly higher exam scores and higher median assessment scores compared to sections without a visual literacy intervention. The online section did not show significant improvements in visual literacy or academic success due to a lack of reinforcement of visual literacy following the initial intervention. The visual literacy intervention shows promising results in improving student academic success and should be considered for implementation in other general education STEM courses.