The actor portrayed Batman in the 2017 superhero movie, and he wanted to take on the role - which he first played in 2016's "Batman v Superman: Dawn of Justice" - for his children, Violet, 15, Seraphina, 12, and eight-year-old Samuel, who he shares with his ex-wife, Jennifer Garner.
"I did Batman because I wanted to do it for my kids," he told The Hollywood Reporter's "Awards Chatter" podcast. "I wanted to do something that my son would dig. I mean, my kids didn't see Argo."
Affleck - who is to play the Dark Knight again in 2022's "The Flash" - has admitted things didn't all go to plan while making "Justice League", but he insisted being able to wear the iconic Batsuit at his son's birthday party "was worth every moment of suffering" on the motion picture.
"Zack (Snyder) wanted to do a version of the Frank Miller Dark Knight graphic novel series, which is a really good version of that," he continued. "Unfortunately, there are a lot of reasons why things go the way they do in the movie business, and just because your face is on the poster doesn't mean that you're dictating all of those things - and even if you were, that they would go well."
"I wore the suit to my son's birthday party, which was worth every moment of suffering on Justice League."
Affleck - who has been open about his battle with alcoholism and his recovery - also admitted he started "drinking too much" around the time he was shooting the movie, but he now feels "as healthy and good as (he has) ever felt."
"I started drinking too much around the time of 'Justice League' and it's a hard thing to confront and face and deal with," he added. "I've been sober for a while now, and I feel really good - as healthy and good as I've ever felt. And the process of recovering from alcoholism has been really instructive."
"I think it's great for people who aren't alcoholics, you know? Like, 'Be honest. Have integrity. Take accountability. Help other people.' It's a good set of things that they teach you. It took me a little while to get it - I had a few slips, like most people - but I feel really good."