Abstract Background Low‐dose rate brachytherapy is the referent treatment for early‐stage prostate cancer and consists in manually inserting radioactive seeds within the organ to destroy tumorous cells. This treatment is inaccurate leading to side effects. Researchers developed robots to improve this technique. Despite ameliorating accuracy, they cannot be clinically used because of size and acceptability. Therefore, a 6‐DOF parallel and co‐manipulated robot is proposed to meet these requirements. Methods To fulfil the application requirements, a compact design was modelled. The robot's optimal dimensions were defined by establishing kinematics and implementing genetic algorithm. The robot's relevance was evaluated by measuring workspace and needle placement errors. Results The robot fits into a cube of 300 × 300 × 300 mm 3 and provides a free‐singularity workspace of 55 × 55 × 150 mm 3 with a possible end‐effector rotation of 15° and a needle placement error <3 mm. Conclusion The results are promising and prove that our robot fulfils the application requirements and presents a beneficial alternative to the manual procedure.