A soybean cultivar designated SJ919784 with high yield potential, tolerance to Roundup.TM. herbicide, early Group 3 maturity, and resistance to races 3 and 14 of Soybean Cyst Nematode, further including the plants and seeds of the cultivar SJ919784, methods for producing a soybean plant by crossing the cultivar SJ919784 with itself or another soybean plant. The invention also relates to soybean cultivar SJ919784 further comprising one or more single gene traits, and to methods of producing a soybean having such traits by introgression, transformation or mutagenesis. The invention also includes using the soybean cultivar SJ919784 to produce other soybean cultivars, breeding lines, and progeny