Functional endoscopic sinus surgery (FESS) is one of the most frequently performed surgeries in otorhinolaryngology. In current clinical practice, it remains manually operated by surgeons who are trained to hold the endoscope with one hand and may, if necessary, be handed to an assistant, thereby reducing task ergonomics. As existing teleoperated robotic surgical systems are incompatible to FESS in terms of robot structure and set-up, in this article, we present a new robotic system for side-by-side robot-assisted endoscope manipulation to improve the handling precision with minimal distraction to surgeons. The work first summarizes clinical considerations for system design is given which aims for reliable and safe endoscope positioning that adapts to the FESS procedures. The robotic system comprises the following three main components: 1) a novel robotic platform that provides dexterous pre-/intra-operative endoscope positioning; 2) a passive compliant endoscope holder that avoids excessive lens-cavity collision forces in case of misoperations; and 3) a foot-wearable interface to allow hands-free pose adjustment of the endoscope. A set of laboratory tests and four cadaver cases were conducted to evaluate the functional feasibility of the system, with its clinical applicability being further validated by two clinical FESS cases. The results show that the system owned efficient set-up time (mean 3.6 mins) with a short learning curve (mean 3.4 mins) for the surgeon to master the foot-wearable interface. The surgeon was able to perform three-handed procedures (e.g. maxillary antrostomy, tumor resections, bleeding treatment, etc.) alone with minimal obstructions to the existing FESS routine practice. Due to its modular structure, the system also has potential to assist other endoscopic surgeries (e.g. ear surgery and skull base surgery) which also involve endoscope related three-handed procedures.