The centre-back was sent off in the Nations League defeat to Denmark last month to add to the personal torment he has experienced in a challenging year on and off the pitch.
On Thursday night he began to heal the pain with the opening goal in England's 3-0 with against Republic of Ireland, and the honour of being handed the captain's armband for the night.
Southgate said: “With Harry, I was really pleased. I felt that the red card here could bottom everything out.
“You could see on his face when he was walking off the pitch that night how he was just having one of those spells where he must have felt everything was against him.
“I had some good conversations with him and I know his club would have supported him and his club performances were solid after that and I thought it was important to get him back in an England shirt.
“It was lovely moment for him to captain the team and to get the goal as well is a real boost so that was great to see."