Background: Digital technology is increasingly being used to enhance healthcare in various areas of medicine. In the area of serious mental illness (SMI), it is important to understand the special characteristics of target users that may influence motivation and competence to use digital health tools (DHTs), as well as the resources and training necessary for these patients to facilitate the use of this technology. Objective: To conduct a quantitative expert consensus survey to identify key characteristics of target users (patients and healthcare professionals [HCPs]), barriers and facilitators for appropriate use, and resources needed to optimize the use of DHTs in patients with SMI. Methods: A panel of 40 experts in digital behavioral health who met the participation criteria completed a 19-question survey rating predefined responses on a 9-point Likert scale. Consensus was determined using a chi-square test of score distributions across 3 ranges (1-3, 4-6, 7-9). Categorical ratings of first, second, or third line were designated based on the lowest category into which the confidence interval of the mean ratings fell, with a boundary >6.5 for first line. Here, we report experts' responses to 9 questions (265 options) that focused on (1) user characteristics that would promote or hinder the use of DHTs, (2) potential benefits/motivators and barriers/unintended consequences of DHT use, and (3) support and training for patients and HCPs. Results: Among patient characteristics most likely to promote use of DHTs, experts endorsed interest in using state-of-the-art technology, availability of necessary resources, good occupational functioning, and perception of the tool as beneficial. Certain diseaseassociated signs and symptoms (eg, more severe symptoms, substance abuse problems, a chaotic living situation) were considered likely to make it difficult for patients to use DHTs. Enthusiasm among HCPs for DHTs and availability of staff and equipment to support their use were identified as variables to enable HCPs to successfully incorporate DHTs into their practices. The experts identified a number of potential benefits of and barriers to use of DHTs by patients and HCPs. Most experts agreed that both HCPs and patients would need to be trained in the use of these new technologies. Conclusions: These results provide guidance to the mental health field on how to optimize the development and deployment of DHTs for patients with SMI.