Sweet cherry is a highly appreciated fruit, with great economic value, linked not only to production yield but also to quality and beneficial health effects, influencing consumer acceptability. Biostimulants have arrived as innovative agronomical strategies to increase the yield and fruit quality of sweet cherries. This work intends to highlight the effect of the application of two concentrations of seaweed-based (SW) and glycine betaine (GB) biostimulants and their combination, on quality (size, soluble solids content, maturity index, and sensorial characteristics) and antioxidant traits (DPPH, FRAP, and β-carotene). Sweet cherries were harvested from a commercial sweet cherry orchard, grafted on “Saint Lucia” rootstock, located in Resende, Northern Portugal. Biostimulants significantly affected (p < 0.01) fruit size, TSS, and SSC/TA: sweet cherries present higher dimensions, soluble solids content, and an increased maturity index when treated with SW at the highest concentration. The application of biostimulants also improved the sensorial profiles of sweet cherries. Overall appearance and firmness attribute enhanced when fruits were sprayed with both SW treatments, while cherry flavour attribute was stronger with SW at highest concentration and MIX treatment. In addition, cherries treated with Mix treatment had a higher antioxidant capacity.