Background: A high prevalence of poor job satisfaction and high chronic stress is documented for general practitioners (GPs) and non-physician practice staff from various countries. The reasons are multifactorial and include deficits in leadership, communication and workflows. This publicly funded study evaluates the effectiveness of the newly developed participatory, interdisciplinary, and multimodal IMPROVEjob intervention on improving job satisfaction among GPs and practice personnel. Here, we report the baseline characteristics of the participating GPs and practice assistants, focusing on job satisfaction and perceived chronic stress. Methods: The IMPROVEjob study was performed as a cluster-randomised, controlled trial (cRCT) with German GP practices in the North Rhine Region. The IMPROVEjob intervention comprised two leadership workshops (one for practice leaders only; a second for leaders and practice assistants), a toolbox with supplemental printed and online material, and a nine-month implementation phase supported by IMPROVEjob facilitators. The intervention addressed issues of leadership, communication, and work processes. During study nurse visits, participants completed questionnaires at baseline and after nine months follow up. The primary outcome was the change in job satisfaction as measured by the respective scale of the validated German version of the Copenhagen Psychosocial Questionnaire (German COPSOQ, version 2018). Perceived chronic stress was measured using the Trier Inventory of Chronic Stress (TICS- SSCS). Results: Recruitment of 60 practices was successful: 21 were solo, 39 were group practices. At baseline, n = 84 practice owners, n = 28 employed physicians and n = 254 practice assistants were included. The mean age of all participants was 44.4 (SD = 12.8). At baseline, the job satisfaction score in the total sample was 74.19 of 100 (±14.45) and the perceived chronic stress score was 19.04 of 48 (±8.78). Practice assistants had a significantly lower job satisfaction than practice owners (p < 0.05) and employed physicians (p < 0.05). In the regression analysis, perceived chronic stress was negatively associated with job satisfaction (b= −0.606, SE b = 0.082, p < 0.001, ICC = 0.10). Discussion: The degree of job satisfaction was similar to those in other medical professionals published in studies, while perceived chronic stress was markedly higher compared to the general German population. These findings confirm the need for interventions to improve psychological wellbeing in GP practice personnel.