Background: The outcome of non-surgical treatment is generally good, but the treatment course can be long and painful with approximately a quarter of the patients acquiring a nonunion. Both surgical and non-surgical treatment can have disabling consequences such as nerve injury, infection, and nonunion. The purpose of the study is to compare patient-reported outcomes after surgical and non-surgical treatment for humeral shaft fractures. Methods: A pragmatic randomized controlled trial (RCT) is planned with two study groups (SHAFT-Young and SHAFT-Elderly). A total of 287 eligible acute humeral shaft fractures are scheduled to be recruited and randomly allocated to surgical or non-surgical treatment with the option of early crossover due to delayed union. The surgical method within the allocation is decided by the surgeon. The primary outcome is the Disability of Arm, Shoulder, and Hand (DASH) score at 52 weeks, and is assessor blinded. The secondary outcomes are DASH score, EQ-5D-5L, pain assessed by visual analog score, Constant-Murley score including elbow range of motion, and anchor questions collected at all timepoints throughout the trial. All complications will be reported including; infection, nerve or vascular injury, surgical revisions (implant malpositioning, hardware failure, aseptic loosening, and peri-implant fracture), major adverse cardiovascular events, and mortality. Discussion: The SHAFT trial is a pragmatic multicenter RCT, that will compare the effectiveness of the main strategies in humeral shaft fracture treatment. This will include a variety of fracture morphologies, while taking the dilemmas within the population into account by splitting the population by age and providing the orthopedic society with an interval for early crossover surgery. Trial registration: Clinicaltrials.govNCT04574336. Registered on 5 October 2020.