Climate change and a growing world population challenge modern agriculture to maintain sustainable production over time on increasingly scarce arable land. The use of plant biostimulants emerges as a safe and environmentally friendly alternative to improve crop production and yield under these unfavorable conditions. Among all plant biostimulants, higher plant-derived biostimulants (hPDBs) are of special interest, due to all the advantages they have in terms of sustainability, production costs, safety, and mainly due to the diversity of bioactive compounds that compose them. In this work, a novel type of plant biostimulant, based on yellow carrot cell cultures, was developed through biotechnological tools. Using 25 mM Me-β-cyclodextrins (Me-β-CD) and 100 μM methyljasmonate (MJ) as elicitors, the production of bioactive compounds with a described biostimulant effect, mainly phytosterols and phenolic compounds, was increased in cell suspensions. A compositionally stable product, yellow carrot biostimulant (YCB), was prepared, and the evaluation of its biostimulant effect was corroborated by applying it as seed priming on tomato seeds germinated under salinity conditions, resulting in the improvement of germination index (+13%), H2O2 (−13%), MDA (−50%), and proline (+12%) contents, compared with untreated seeds, when the dose of 1% (v/v) YCB was applied. Therefore, we have developed a novel potential biostimulant product based on yellow carrot cell cultures, enriched in phenolic compounds and phytosterols, which has demonstrated its effect on tomato seeds subjected to salt stress.