O.C.G.A. § 16-3-21
Use of force in defense of self or others; evidence of belief that force was necessary in murder or manslaughter prosecution
(a) A person is justified in threatening or using force against another when and to the extent that he or she reasonably believes that such threat or force is necessary to defend himself or herself or a third person against such other's imminent use of unlawful force; however, except as provided in Code Section 16-3-23, a person is justified in using force which is intended or likely to cause death or great bodily harm only if he or she reasonably believes that such force is necessary to prevent death or great bodily injury to himself or herself or a third person or to prevent the commission of a forcible felony.
(b) A person is not justified in using force under the circumstances specified in subsection (a) of this Code section if he:
(1) Initially provokes the use of force against himself with the intent to use such force as an excuse to inflict bodily harm upon the assailant;
(2) Is attempting to commit, committing, or fleeing after the commission or attempted commission of a felony; or
(3) Was the aggressor or was engaged in a combat by agreement unless he withdraws from the encounter and effectively communicates to such other person his intent to do so and the other, notwithstanding, continues or threatens to continue the use of unlawful force.
(c) Any rule, regulation, or policy of any agency of the state or any ordinance, resolution, rule, regulation, or policy of any county, municipality, or other political subdivision of the state which is in conflict with this Code section shall be null, void, and of no force and effect.
(d) In a prosecution for murder or manslaughter, if a defendant raises as a defense a justification provided by subsection (a) of this Code section, the defendant, in order to establish the defendant's reasonable belief that the use of force or deadly force was immediately necessary, may be permitted to offer:
(1) Relevant evidence that the defendant had been the victim of acts of family violence or child abuse committed by the deceased, as such acts are described in Code Sections 19-13-1 and 19-15-1, respectively; and
(2) Relevant expert testimony regarding the condition of the mind of the defendant at the time of the offense, including those relevant facts and circumstances relating to the family violence or child abuse that are the bases of the expert's opinion.