Chronic joint pain is associated to an increase in the consumption of medication and decrease in life quality in elderly people, which requires developing non-pharmacological treatments. The aim of this study was to evaluate the effectivity of a group intervention, based on animal-assisted therapy and applied to elderly people with chronic joint pain and polymedication, regarding the decrease of chronic pain, use of analgesics and improvement of life quality. A randomized controlled trial, two arms and open-label was conducted in a Primary Health Center. Twelve weekly sessions of kinesitherapy; in the EG, these exercises were performed with the additional assistance of the therapy dog. A total of 52 participants (22 Control Group (CG), 30 EG), average age 77.50 (±7.3), women 90.4%. A significant reduction on post-intervention values of pain β = −0.67(−1.27, −0.08), p = 0.03 and pain induced insomnia β = −0.53(−1.01, −0.05), p = 0.03 was found in EG for increasing baseline values. Animal-assisted therapy leads to an additional reduction in the perception of pain and pain induced insomnia in individuals with higher baseline severity. The presence of the dog improves the attachment to intervention and the satisfaction of the participants.