A novel ultra-wideband (UWB) reflectarray antenna for the Internet of Vehicles (IoV) is introduced in this paper. By simply connecting the neighboring reflectarray elements, the proposed reflectarray antenna achieves a remarkable radiation pattern bandwidth of 20 GHz, ranging from 10 GHz to 30 GHz. To explain the operating principles of the proposed reflectarray antenna, the equivalent circuit (EQC) model of the unit cell is built, which also provides an efficient and rapid way to analyze the performance of the proposed reflectarray element. It is found from the EQC analysis that the connected elements can achieve better reflection phase responses than conventional separated elements, thereby improving the array bandwidth. As a proof of concept, a 503-element reflectarray antenna simultaneously covering the vehicle-to-satellite bands (12.25–12.75 GHz/14.0–14.5 GHz/19.6–21.2 GHz/29.4–31.0 GHz), the 24-GHz short-range vehicle radar band (24.25–26.65 GHz) and the 5G millimeter-wave band (27.5–28.35 GHz) is designed, fabricated, and characterized. The experimental results demonstrate that the presented reflectarray antenna can maintain undistorted beams, high antenna gain, low cross-pol level, and moderate aperture efficiency over a bandwidth of 100%, i.e., from 10 to 30 GHz. With its simple and planar aperture as well as excellent performance, the proposed reflectarray antenna can be a promising candidate for vehicles that require reliable high data-rate satellite links and 5G millimeter-wave connections simultaneously.