This paper investigates the frequency support capability of a grid-integrated, utility-scale hybrid power plant (HPP) comprising a wind power plant (WPP), solar power plant (SPP), and a battery energy storage system (BESS). The study focuses on the provision of ancillary frequency services, specifically frequency containment reserve and fast frequency reserve as defined by the market in the East Denmark bidding zone (DK2). The HPP is modeled in MATLAB/Simulink and Simscape and integrated into an IEEE 9-bus system, which is slightly modified to capture the desired characteristics of strong and weak grid conditions. In this modified IEEE 9-bus system, one of the generators is replaced by the HPP model to assess the grid frequency response to frequency disturbances. The simulation results show that, under weak grid conditions, the modified IEEE 9-bus system with only conventional generators provides more effective frequency support than the same system with one generator replaced by an HPP using grid-following control. To address this limitation of the HPP, a grid forming (GFM) control strategy is implemented to the BESS within the HPP. The results demonstrate that GFM control in the BESS significantly improves the HPP’s capability to support the grid frequency under weak grid conditions.