Ocean temperature is a key determinant of the distribution and phenology of marine life, particularly poikilotherms. We examined effects of ocean temperature on nesting phenology and fecundity for Loggerhead Sea Turtles (Caretta caretta) in the northern Gulf of Mexico using long-term nesting survey data from northwest Florida. The first clutch of the year was deposited earlier when sea surface temperature in months prior to the nesting season was warmer and this resulted in a longer nesting season. Nest abundance and clutch size were associated with the monthly mean temperature just prior to the nesting season, with higher fecundity occurring in warmer years. Higher nest success was associated with higher February temperature and lower May temperature. Median nest date was not associated with monthly temperature prior to the nesting season. Our results provide further details about the impacts of the thermal environment on Loggerhead Sea Turtle life history and suggest that altered ocean temperatures may affect phenology and fecundity of marine poikilotherms.