The focus of this research is the investigation of steady state fully developed mixed convection flow in a chemically reacting fluid (exothermic fluid) in the presence of Casson fluid across a vertical tube. Subject to suitable boundary conditions, the temperature and velocity equations are solved in non-dimensional form employing regular perturbation approach. The basic flow patterns of temperature and velocity flow are explored as an implication of controlling characteristics such as chemical reaction parameter, Casson fluid parameter, mixed convection parameter and constant pressure gradient. The findings are carefully investigated and graphically represented with the help of illustrative graphs. It was observed that raising the value of the positive mixed convection parameter enhances the fluid velocity while the negative mixed convection parameter suppresses the fluid flow. Additionally, increasing the values of chemical reaction parameter is noticed to improve the fluid temperature and velocity respectively, whereas increasing Casson parameter tends to suppress the fluid velocity.