We demonstrate a novel technique for locking and tuning of a near-degenerate nanosecond optical parametric oscillator (OPO) using a transversely chirped volume Bragg grating. When the grating was translated, the OPO signal wavelength could be tuned from $1011\text{to}1023\mathrm{nm}$ $\left(3.5\mathrm{THz}\right)$ . The OPO was based on a periodically poled $\mathrm{K}\mathrm{Ti}\mathrm{O}\mathrm{P}{\mathrm{O}}_4$ as a nonlinear crystal and was pumped at $532\mathrm{nm}$ with up to $1.9\mathrm{mJ}$ of energy. The generated signal at an energy of $0.37\mathrm{mJ}$ had a bandwidth of $0.50\mathrm{nm}$ and a suppression of broadband background of $>30\mathrm{dB}$ . The demonstrated technique is widely applicable for the construction of narrowband tunable sources.