Hypertension phenotypes may represent differential pathophysiologic mechanisms and clinical impact, yet they have been poorly investigated. The study aimed to examine the associations of physical activity and sedentary behavior with hypertension phenotypes in a large group of Greek children and to identify thresholds regarding risk of hypertension. This was a cross-sectional study with a regionally representative sample of 2473 schoolchildren aged 9-13 years, with full data on physical activity and sedentary behavior indices, as well as arterial blood pressure measurements, physical examination, and anthropometry. Hypertensive children of both sexes had lower levels of physical activity (steps/d). Hypertensive girls had lower moderate-to-vigorous physical activity (MVPA), whereas hypertensive boys with isolated systolic hypertension (ISH) had more screen time than their normotensive counterparts. Increased levels of physical activity was associated with 33%-54% lower risk of all hypertension phenotypes in both sexes, whereas increased MVPA was associated with 41%-65% lower risk of all phenotypes in girls and with ISH and systolic and diastolic hypertension (SDH) in boys. In boys, higher sedentary time was associated with 11%-13% higher risk for SDH and ISH. Cutoff points of 12,378 steps/d, 47.3 min/d of MVPA, and 2.9 h/d of sedentary behavior were determined for identifying children at increased risk of hypertension. Physical activity is inversely associated with all hypertension phenotypes, whereas sedentary behavior is positively associated with ISH and SDH in boys. More studies should confirm the hypertension-specific cutoff values identified to be used in future prevention programs for childhood hypertension.