BACKGROUND: Generally, there is limited information on longitudinal trends and the interrelations between physical activity (PA), problematic gaming behavior (PGB), described as a dysfunctional pattern of videogame activities, and quality of life (QoL) based on data that include measurements from both pre- and postpandemic onset. This is also the case for university students. As society faced unprecedented restrictions during this period, these aspects may have developed unfavorably. OBJECTIVE: To examine PA, PGB, and QoL among Norwegian University students prior to and during the initial stages of the pandemic and assess their temporal interrelations. METHOD: The data are derived from the "Students' Psychological Health Over Time" study (SPOT). Linear mixed models were used to examine the development from January 2020 to November 2020 over three time points for the total sample and across gender. A traditional cross-lagged panel model analysis was used to estimate temporal associations. Age, gender, socioeconomic status, and partner status were included as covariates. FINDINGS: PA and QoL decreased linearly over time (Cohen's d = 0.12 and 0.35, respectively), while only male students reported a small reduction in PGB (Cohen's d = 0.03). PA levels decreased considerably more for male students than female students (Cohen's d = 0.17 and 0.09, respectively). There was a small reciprocal negative temporal association between PA and PGB (standardized β = -0.04 and -0.05, respectively). All other temporal associations were not statistically significant in the adjusted analysis. CONCLUSION: The findings highlight gender-variant negative developments in PA and QoL and suggest a negative reciprocal interrelation between PA and PGB. The findings point to potential adverse health effects that should be taken into account when restrictive pandemic measures are considered.