"That was the only time in my life that I ever considered suicide."
Smith is seen in the trailer for the series writing his memoirs, exercising and sitting around a table with his children Trey, 28, Willow, 20, and Jaden, 23.
Willow appears emotional, while her brothers and others at the table look on quietly.
It's not clear at what stage of Smith's life that he encountered suicidal thoughts.
During the emotionally raw revelation Smith can be seen wiping back the tears as his family listens on.
His emotional confession comes after wife Jada Pinkett-Smith opened up about her bedroom struggles.
During an episode of Red Table Talk, Jada told Goop founder Gwyneth Paltrow that she struggles with not getting what she "wants" sexually from Will. She also admitted she struggles to know what she likes sometimes.
She revealed: "It's hard.
"The thing Will and I talk about a lot is the journey. We started in this at a very young age, you know, 22 years old.
"That's why the accountability part really hit for me because I think you expect your partner to know [what you need], especially when it comes to sex."
She continued: "It's like, 'Well, if you love me, you should know. If you love me, you should read my mind.' That's a huge pitfall."
The doco airs on November 8.
Where to get help: • Lifeline: 0800 543 354 (available 24/7) • Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7) • Youthline: 0800 376 633 or text 234 (available 24/7) • Kidsline: 0800 543 754 (available 24/7) • Whatsup: 0800 942 8787 (12pm to 11pm) • Depression helpline: 0800 111 757 or text 4202 (available 24/7) • Anxiety helpline: 0800 269 4389 (0800 ANXIETY) (available 24/7) • Rainbow Youth: (09) 376 4155 If it is an emergency and you feel like you or someone else is at risk, call 111.