Recent studies indicate that back diseases are increasing annually due to various factors such as poor lifestyle habits, aging, pregnancy, and accidents. Patients with such conditions often experience difficulty in managing their backs, leading to a lower quality of life as they endure back pain when sitting for prolonged periods or when transitioning between sitting and standing positions. Sit-to-Stand (STS) movement is particularly challenging for these patients. In response, this study proposes a variable assist chair that supports the user's STS movements. Non-powered assist chairs using the first-class lever mechanism can be advantageous due to their light weight and low cost. Additionally, the chair's variable design enables it to be universally applicable across a wide range of environments and users. This research demonstrates the effectiveness of the new mechanism in assisting users’ transitions between sitting and standing positions. Furthermore, it highlights the need for further research to explore the applicability of the mechanism to a diverse range of users.