Dog ownership has been associated with increased levels of physical activity (PA), including increases in total PA and walking time in some but not in all studies. These earlier studies did not consider puppy acquisition, in particular, and were limited to a maximum of 10 months duration. The purpose of the current pilot study was, therefore, to analyze long-term changes in participants’ PA behavior after puppy acquisition. Participants who acquired a puppy from one of nine preselected breeds differing in size and energy level were included. PA was assessed at baseline and 6, 12, 24 and 36 months after puppy acquisition using an online questionnaire. Participants, who were initially included, did not differ in their PA at baseline (n = 38). In the group that completed the trial (n = 11) total PA, leisure time walking, total dog-related PA, and total dog walking increased within the first two years and decreased while remaining above baseline values during the last year, coinciding with the COVID-19 pandemic. Non-dog-related PA did not change over time. We conclude that the acquisition of a puppy increases PA and thus, could have a long-lasting positive effect on physical health.