Excess growth hormone (GH) has been implicated in multiple cancer types and there is increasing interest in the development of therapeutic inhibitors targeting GH–GH receptor (GHR) signalling. Here we describe a panel of anti-GH monoclonal antibodies (mAbs) generated using a hybridoma approach and identify two novel inhibitory mAbs (1-8-2 and 1-46-3) that neutralised GH signalling. mAbs 1-8-2 and 1-46-3 exhibited strong inhibitory activity against GH-dependent cell growth in a Ba/F3-GHR cell viability assay, with EC₅₀ values of 1.00 ± 0.27 and 0.5 ± 0.1 µg/mL, respectively. Cross-reactivity with the human placental hormones, placental lactogen (PL) and placental GH, was observed by ELISA, but neither antibody cross-reacted with mouse GH or human prolactin (PRL). mAb 1-8-2 had a binding affinity for GH of K_D 0.62 ± 0.5 nM, while mAb 1-46-3 had a K_D of 2.68 ± 0.53 nM, as determined by bio-layer interferometry. mAb 1-46-3 inhibited GH-dependent signal transduction in T-47D and LNCaP cancer cell lines and reduced GH-dependent cell growth and migration in the breast cancer cell line T-47D. mAb 1-46-3 inhibited T-47D cell viability more effectively than the GHR antagonist B2036. In conclusion, we describe two novel inhibitory anti-GH mAbs and provide in vitro evidence supporting development of these entities as anti-cancer therapeutics.