The German defender played just 42 games in five seasons at Chelsea, and was beset by injuries in the first 18 months on Teesside.
Now Huth is finally finding top gear and Southgate enthused: "It's terrific to have Robert playing regularly with us and beginning to find his full fitness.
"It's been a really frustrating time for him here because nothing has gone right for him since he joined us.
"It took us a long time to get to the crux of his injury problem, but we did that last summer, and now he is reaping the benefits."
Southgate believes that Huth's developing stature on the pitch will fully justify the decision to accept a £7m fee from Spurs from Jonathan Woodgate.
The Boro boss told the Evening Gazette: "You have to make major decisions at times and I felt that we had so much cover in that position.
"Huth is starting to show so much strength on the field. He's a really positive character.
"Watching him every day in training you can see that he is getting better and better.
"It's terrific to see and it creates a very healthy situation for us because we've been looking very strong at the back lately."