The Manchester United defender was sent off after just 31 minutes on Wednesday night as England lost 1-0 to Denmark.
Christian Eriksen scored the only goal of the game from the penalty spot on a disappointing night for England, which saw them slip to third in their Nations League Group A2.
The Three Lions’ tough night was summed up by Maguire, who was sent off after picking up two yellow cards in 31 minutes.
The dismissal is the latest blow to Maguire, who was involved in an altercation with police in Mykonos in August that led to him being removed from the England squad then.
Southgate is convinced the defender will bounce back and has assured him that he has the squad’s full support.
“He has had a difficult period and in these periods you learn a lot about yourself, you learn a lot about other people,” said Southgate.
“You learn who is there for you in those difficult times. He will come through it. He will be a better player and a stronger man for it.
“He knows there will be criticism after this and you have to accept that. To go down to 10 men is costly for the team.
“But we fully back him, we fully support him. He has been a top player and is a top player. He will come through it.
“He showed on Sunday why we think so much of him with his performance against Belgium. As I say, he will get through this period and he will be back to his best.”
Given what Maguire has been through this summer, and the scrutiny on him now, it has been suggested perhaps the centre-back needs a break from football.
But Southgate has backed the 27-year-old to come through his troubles and is currently not planning to omit him from his England squad next month.
“I think knowing Harry as I do, he will want to play football,” said Southgate. “The best place for him to be is on the pitch.
“I said earlier, he is having to deal with everybody having an opinion on what he should be doing, what he isn’t doing, what he is doing.
“That is life as a top player. If nobody is interested in you then life is very straight forward. If you are captain of Manchester United and a top player for England then everybody has a view, everybody has an opinion.
“You have to ride with that, but he is strong enough to deal with it. He has got a little spell at the moment where a lot of things are going against him, but he has got to show the resilience I know he has to come through that.”