There are high rates of tobacco smoking among people who experience mental illness (MI). While videos are an effective method of disseminating health-related information, there is limited research investigating the effectiveness of video-delivered education promoting smoking cessation among people living with MI. This formative study aimed to investigate the effectiveness and acceptability of targeted video resources providing smoking cessation information and advice to smokers with MI. This study used a mixed-method design; 29 Australian smokers living with MI completed a preinterview survey including 12 questions assessing knowledge about smoking cessation, watched six videos developed by the research team providing information about smoking cessation, took part in semistructured interviews about the videos' quality, content, and format, and then completed a postinterview survey identical to the preinterview survey to assess changes in smoking cessation-related knowledge. A Wilcoxon signed rank test was used to calculate changes in cessation-related knowledge, and thematic analysis was used to identify common themes in qualitative data. We found a statistically significant increase in participants' smoking cessation-related knowledge scores after watching the videos. Participants indicated an overall high level of acceptability of the videos' quality, content, and format, and findings from the semistructured interviews reflected these favorable views. This study's findings provide a new understanding of the effectiveness and acceptability of customized video-based education to promote smoking cessation among people living with MI, and can be used to inform the content and focus of video resources aimed at increasing knowledge about smoking cessation for people experiencing MI.