BackgroundPhysical exercise, a cornerstone of the conservative management of knee osteoarthritis (KOA), is exhaustively recommended by important clinical guidelines. A strength therapeutic exercise program (STEP) relieves pain, improves physical function and ultimately ameliorates quality of life (QoL). Furthermore, photobiomodulation (PBM) has been used as an adjunct treatment for people with KOA; however, there are still controversial recommendations regarding its use on this population. Thus, we hypothesised that PBM, when associated with a STEP protocol on patients with KOA, could induce better clinical outcomes than a STEP protocol alone.Methods and analysisThe study is a 6-month triple-blind placebo-controlled randomised clinical trial with intention-to-treat analysis. The trial will include 120 people with clinic and radiographic signs of KOA. The intervention consists of a supervised STEP and PBM protocols conducted over an 8-week intervention period. Assessments are performed at baseline, right after treatment, and 3-month and 6-month follow-up periods. The primary clinical outcome is pain intensity according to a 10 cm Visual Analogue Scale. Secondary outcomes are the global Western Ontario & McMaster Universities Osteoarthritis Index; QoL assessed by the 36-item Short-Form health survey questionnaire; and performance-based physical parameters assessed by the 30 s chair stand test; the stair climb test; and the 40 m fast-paced walk test.Ethics and disseminationThe trial was approved by the Human Research Ethics Committee of the Federal University of São Carlos, São Paulo, Brazil (REC no 2.016.122). Results will be published in peer-reviewed journals.Trial registration numberBrazilian Clinical Trials Registry (U1111-1215-6510).