Microbial-based biostimulants containing arbuscular mycorrhizal fungi (AMF), Trichoderma fungi and plant growth-promoting rhizobacteria (PGPR) have been applied in an open-field tomato cultivation. A two-years field experiment (2020-2021) was performed in Southern Italy on “Heinz 1534” processing tomato hybrid, using three commercial formulations characterized by different microbial consortia (MIC: Glomus spp., Rhizophagus spp., Bacillus spp., Streptomyces spp., Pichia spp., Trichoderma spp.; EKO: Glomus spp., Bacillus spp., Streptomyces spp., Pseudomonas spp., Arthrobotrys spp., Monacrosporium spp., Paecilomyces spp., Myrothecium spp., Trichoderma spp.; FID: Glomus spp., Bacillus spp., Trichoderma spp.) and comparing them to untreated control (CTRL). The effect of growing season and microorganism-based treatments on yield, technological traits and functional quality of tomato fruits was assessed. The year of cultivation (Y) affected yield (with lower fruit weight, higher marketable to total yield ratio and higher % of total defected fruits in 2020), and technological components (higher dry matter, total acidity, total soluble solids in 2020). During the first year of the trial, all evaluated treatments (MIC, EKO and FID) enhanced soluble solids content by 10%, on average, compared to CTRL. Sucrose and lycopene contents were influenced both by the microbial-based treatments and the growing season (greater values found in 2021 with respect to the first year). Y factor also significantly affected all evaluated metabolites contents, except for tyrosine, essential (EAA) and branched-chain (BCAAs) amino acids. Over two years of field trial, FID biostimulant enhanced the contents of proteins (+53.71%), alanine (+16.55%), aspartic acid (+31.13%), γ-aminobutyric acid (+76.51%), glutamine (+55.17%), glycine (+28.13%), monoethano-lamine (+19.57%), total amino acids (+33.55), essential amino acids (+32.56%) and branched-chain amino acids (+45.10%) compared to the untreated control. Our findings highlighted the valuable effect of FID microbial inoculant in boosting several primary metabolites (proteins and amino acids) in the fruits of processing tomato crop grown under Southern Italy environmental condi-tions, although no effect on yield and its components was appreciated.