Peri-implantitis is an inflammatory condition that involves the loss of attachment and support around dental implants. In this case report, a middle-aged woman presented with two implants in the mandibular right quadrant that were diagnosed with peri-implantitis. The patient also had tenderness around the implants and reported sensitivity when performing oral hygiene procedures. Surgical treatment comprised a free gingival graft to augment the keratinized tissue width around the implants, followed by a second procedure of implantoplasty and surface decontamination. The outcome showed radiographic resolution of the peri-implant defect around the premolar implant with a marked increase of keratinized tissue (> 4 mm) around both implants after 1 year of follow up. On a patient level, significantly reduced sensitivity around the implants and better home care were reported. This case report showed that the increase of keratinized tissue may benefit the clinical and patient outcomes of peri-implantitis treatment in terms of decreased probing depths, absence of inflammation, and improved radiographic crestal stability. The combined correction of both hard and soft tissue defects around peri-implantitis lesions may facilitate treatment success and help maintain peri-implant stability.