This study will evaluate the long-term safety and tolerability of NBI-1065845 as an adjunctive treatment in participants with MDD.

Key Inclusion Criteria:

• Participant has a primary diagnosis of recurrent MDD (moderate or severe) or persistent depressive disorder.
• Participant has had an inadequate response to oral antidepressant treatments in the current episode of depression.
• Participant must have been taking oral antidepressants for at least 8 weeks prior to screening.
• Willing and able to comply with all study procedures and restrictions in the opinion of the investigator.

Key Exclusion Criteria:

• A current or prior psychiatric disorder diagnosis in the last 1 year that was the primary focus of treatment other than MDD.
• Are considered by the investigator to be at imminent risk of suicide or injury to self or others.

Other protocol defined inclusion and exclusion criteria apply.