The strategic formation of partnerships for leveraging sport events to achieve social impact is becoming a critical component of large-scale sport events. The authors know less about the process dimensions related to the formation and collaborative dynamics of a sport event–leveraging partnership. To address this gap, the authors focus on examining the formation and collaborative dynamics alongside the challenges of the cross-sector partnership, the Ontario Parasport Legacy Group (OPLG), which emerged as an important leveraging strategy for the Toronto 2015 Pan/Parapan American Games. The authors found that the formation of the OPLG was shaped through broader environmental elements—including resource conditions, window of collaborative opportunity, and cultural influence—and essential drivers of strategic leadership and consequential incentives. Furthermore, the authors’ analysis shows that the development of the OPLG and its effectiveness in partnership delivery were determined through key domains of collaborative dynamics (i.e., engagement, motivation, and joint capacity).