An antibacterial scaffold is highly desirable to prevent bacterial infection in orthopedic treatment. In this work, silver was in situ grown in mesoporous bioactive glass (MBG) to endow a polymer scaffold with sustained antibacterial activity. In detail, MBG was firstly modified by the oxidative self-polymerization of dopamine (denoted as pMBG). Then, pMBG was used to capture silver ions into the mesoporous channel via coordination reaction and further in situ reduce silver ions to metallic silver by the redox reaction of the catechol groups. Finally, the Ag loaded pMBG (Ag@pMBG) was introduced into polymer matrices to construct composite scaffold by additive manufacturing technology. The antibacterial tests showed that the composite scaffold exhibited robust antibacterial activity with an inhibition ring of 24.2 mm and bacterial inhibition rate more than 99% against Escherichia coli. Moreover, ion release behavior demonstrated that the composite scaffold could continually release Ag over 28 days. Besides, the composite scaffold also showed good cytocompatibility in facilitating osteoblast adhesion and proliferation.