(1) Introduction: Tendinous mallet finger is a frequent deformity that occurs after an extensor tendon injury during sports or daily life activities. Despite the existence of numerous non-operative and operative techniques to address this deformity, there is a controversy on its optimal management. In this study, we aimed to present a direct tendon suture technique using the distal interphalangeal (DIP) joint open approach for treating tendinous mallet finger injury. (2) Methods: Between 2019 and 2021, 19 patients with closed non-fracture tendinous mallet fingers underwent the direct tendon and paratenon repair technique. After skin incision, we opened the paratenon with lazy S shape incision and found the ruptured proximal and distal tendon ends. We reapproximated the tendons using a simple interrupted suture with Prolene #6/0. After that, we meticulously performed paratenon repair using PDS #6/0 for preventing readherence. Temporary trans-articular Kirschner wire fixation was used for 4 weeks. (3) Results: All patients were followed-up for 3–8 months (mean: 4.8 months). The mean final extension lag was 6.5 degrees, and the overall rate of cases with excellent and good outcomes using Crawford’s criteria was 85%. (4) Conclusions: In conclusion, this surgical approach could be a reliable alternative for the treatment of tendinous mallet finger injuries.