Post-traumatic stress disorder (PTSD) is a common mental illness. Treatments for PTSD are regarded as highly effective, but a large-scale, prospective, longitudinal randomized controlled trial comparing the effectiveness of these treatments has been requested by the research community. This study aims to conduct a comprehensive investigation into the effectiveness of two prominent PTSD therapies, eye movement desensitization and reprocessing (EMDR) and cognitive therapy for PTSD (CT-PTSD), within the Norwegian specialist health care services. The study aims to compare the therapy effectiveness, including their impact on comorbid disorders, complex PTSD symptoms, and functional outcomes post-treatment. Patients will be randomly assigned to EMDR or CT-PTSD and given manualized therapy aligned with their treatment goals. Each arm aims to recruit 135 patients, resulting in a total sample size of 270 patients. The main objective of this study is to examine the growth curves of the two methods and how patient characteristics affect their developments. Secondary short-term aims include (1) investigating the impact of EMDR and CT-PTSD on complex PTSD symptoms, (2) assessing effects on other clinical conditions and functional outcomes, and (3) exploring whether the therapeutic alliance mediates treatment effects. Secondary long-term aims are (1) to assess the long-term effects of EMDR and CT-PTSD on PTSD symptoms and (2) to explore the impact of extended or additional treatments on outcomes.