Tissue-engineered hydrogels hold great potential as nucleus pulposus substitutes (NP), as they replicate the native 3D environment. Methacrylated gellan gum hydrogels, which can be ionic- (iGG-MA) or photo-crosslinked (phGG-MA), have been proposed as biomaterials for NP regeneration. In this study, the mechanical stability and biological performance of these hydrogels were evaluated in vitro. Human intervertebral disc (hIVD) cells obtained from herniated patients were cultured within both hydrogels, up to 21 days. The mechanical properties were investigated under dynamic mechanical analysis after specific times of culturing. In addition, biological characterization was performed in terms of cell viability (Live/dead assay and DNA quantification), production of a cartilage-like tissue by histological staining and expression of typical chondrogenic markers and specific NP-markers through immunocytochemistry. Results demonstrated that after 21 d of culturing, hIVD cells were viable and the E’ of iGG-MA (115.8 ± 21.6 kPa) and phGG-MA (98.4 ± 0.3 kPa) hydrogels was higher than that observed for acellular hydrogels (80.4 ± 20.6 and 85.8 ± 4.2 kPa, respectively). The increase observed in E’ value during in vitro culturing is consistent with the viability and production of extracellular matrix by hIVD cells, as demonstrated by the evaluation of biological performance. The results presented in this study also indicate that the iGG-MA and phGG-MA hydrogels are stable and non-cytotoxic in vitro, present adequate mechanical properties and support hIVD cells encapsulation and viability, thus possessing promising properties for being tested in cellular-based tissue engineering strategies aimed to restore the functionality of NP.