An organometallic compound represented by Formula 1: wherein, in Formula 1, M 11 is selected from a first-row transition metal, a second-row transition metal, and a third-row transition metal; R 11 to R 18 are each independently selected from a hydrogen, a deuterium, -F, - Cl, -Br, -I, a hydroxyl group, a cyano group, a nitro group, a carbonyl group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 30 alkyl group, a substituted or unsubstituted C 3 -C 30 branched alkyl group, a substituted or unsubstituted C 2 -C 30 alkenyl group, a substituted or unsubstituted C 2 -C 30 alkynyl group, a substituted or unsubstituted C 1 -C 30 alkoxy group, a substituted or unsubstituted C 3 -C 10 cycloalkyl group, a substituted or unsubstituted C 1 -C 10 heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10 cycloalkenyl group, a substituted or unsubstituted C 1 -C 10 heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 30 aryl group, a substituted or unsubstituted C 6 -C 30 aryloxy group, a substituted or unsubstituted C 6 -C 30 arylthio group, a substituted or unsubstituted C 7 -C 30 arylalkyl group, a substituted or unsubstituted C 1 -C 30 heteroaryl group, a substituted or unsubstituted C 2 -C 30 heteroaryloxy group, a substituted or unsubstituted C 2 -C 30 heteroarylthio group, a substituted or unsubstituted C 3 -C 30 heteroarylalkyl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and a substituted or unsubstituted C 1 -C 30 alkylsilyl group; optionally, adjacent two of R 11 to R 15 are linked to form a substituted or unsubstituted saturated ring, or a substituted or unsubstituted unsaturated ring; at least one of R 11 to R 15 is selected from a substituted or unsubstituted C 3 -C 30 branched alkyl group, a substituted or unsubstituted C 3 -C 10 cycloalkyl group, a substituted or unsubstituted C 1 -C 10 heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10 cycloalkenyl group, a substituted or unsubstituted C 1 -C 10 heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 30 aryl group, a substituted or unsubstituted C 6 -C 30 aryloxy group, a substituted or unsubstituted C 6 -C 30 arylthio group, a substituted or unsubstituted C 7 -C 30 arylalkyl group, a substituted or unsubstituted C 1 -C 30 heteroaryl group, a substituted or unsubstituted C 2 -C 30 heteroaryloxy group, a substituted or unsubstituted C 2 -C 30 heteroarylthio group, a substituted or unsubstituted C 3 -C 30 heteroarylalkyl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and a substituted or unsubstituted C 1 -C 30 alkylsilyl group; R 19 and R 20 are each independently selected from a hydrogen, a deuterium, a C 1 -C 30 alkyl group, and a deuterium-substituted C 1 -C 30 alkyl group; at least one of R 11 to R 20 is a deuterium-containing substituent; n11 is selected from 1, 2, and 3; L 11 is selected from a monodentate ligand and a bidentate ligand; and m11 is selected from 0, 1, 2, 3, and 4.