Among the exciting recent advances in the field of carbon-based nanomaterials, the successful realization of a carbon nanoribbon composed of 4–5–6–8-membered rings (ACS Nano 2023 17, 8717) is a particularly inspiring accomplishment. In this communication motivated by the aforementioned achievement, we performed density functional theory calculations to explore the structural, electronic and mechanical properties of the pristine 4–5–6–8-membered carbon nanoribbons. Moreover, we also constructed four different nitrogen-terminated nanoribbons and analyzed their resulting physical properties. The acquired results confirm that the pristine and nitrogen-terminated nanoribbons are are thermally stable direct-gap semiconductors, with very close HSE06 band gaps between 1.12 and 1.25 eV. The elastic modulus and tensile strength of the nitrogen-free 4–5–6–8-membered nanoribbon are estimated to be remarkably high, 534 and 41 GPa, respectively. It is shown that nitrogen termination can result in noticeable declines in the tensile strength and elastic modulus to 473 and 33 GPa, respectively. This study provides useful information on the structural, thermal stability, electronic and mechanical properties of the pristine and nitrogen-terminated 4–5–6–8-membered carbon nanoribbons and suggests them as strong direct-gap semiconductors for electronics, optoelectronics and energy storage systems.