Muscle weakness following a stroke, spinal cord injuries or age can make people sedentary temporarily or permanently. The best strategy for such patients' recovery is to motivate them to break their wheel/chair bound condition and attempt independent motion. The ability to easily transition from sit-to-stand (STS) would encourage further mobility. Hence, there is a need for wearable assist devices that seamlessly assists STS transition. Such a device should be non-obstructive during the seated phase and assist during STS. Soft exosuits are advantageous over conventional rigid exoskeletons in this context. The use of exosuits in STS assistance is currently limited by the lack of low-profile soft actuators with high strain rate and force-to-weight ratio. Hence, we propose a novel low-profile vacuum actuator that, can be rapidly fabricated, is lightweight (14 g), and can provide high strain (~65%) and a high force-to-weight ratio (~160). The proposed actuator comprises a low-profile spring encased within a low-density polyethylene film with rapid vacuum actuation and passive quick return. The applicability of the proposed actuator in assisting STS is preliminarily studied via a prototype exosuit. Surface electromyography (sEMG) measurements of the gluteus maximus (GM) muscles during STS experimentally show the potential use of the proposed actuator in an STS-assist exosuit. Experimental sEMG results indicate a mean reduction of ~46% muscle activity of GM muscle during STS.