Though Industry 4.0 automation has replaced the human workforce by machines in industries, physical workers are indispensable in many facilities. One primary source of stress in the manufacturing workplace is inappropriate work content (e.g., unreasonable workload and work pace). With workers facing physical activities or machine operations, work-related stress can affect their performance and cause productivity, quality, and safety problems. Industrial managers constantly seek ways to ease stress among workforce, as Healthy Operator is proposed as an essential pillar of the Operator 4.0 concept. As the first step of stress reduction is to identify the stress (if possible, its early signs), heart rate variability (HRV) is widely measured, with different methods adopted to assess the stress levels of workers. Recent technological advancements have developed many non-invasive measurement techniques and systems, offering more convenience and flexibility than traditional clinical methods. Since human centricity is a strategic focus of the forthcoming Industry 5.0 initiative proposed by the European Union, these measurement practices should be disseminated and shared to foster better stress identification and reduction. A systematic literature review is needed to deliver a comprehensive update in the field. Besides synthesizing the relevant development, the review study aims to motivate industrial managers to adopt a similar approach and provide helpful guidance on what to expect with the Heart Rate Variability measurement for the workplace stress assessment. A detailed protocol for the systematic literature review is given.