The Three Lions came through their qualifying campaign with aplomb, winning nine of their ten group games before seeing off Croatia in a play-off to secure a place at the Finals in Czech Republic this June.
Southgate has enjoyed working with a relatively settled squad throughout, with 32 different players featuring during the 12 qualifying matches.
And with many of his charges finding themselves in good form and catching the eye in the Premier League, Southgate believes the majority of his squad picks itself.
"If I had to pick a squad tomorrow I would know pretty much what it would be," he admitted.
"You think picking 23 is going to be difficult but actually we’ve had quite a settled group for a long period of time.
"But there might be one or two that emerge late from that, boys like Jesse Lingard who has just started to get fit again which is great to see."
Over the last 18 months, a number of Southgate’s squad have been picked by Roy Hodgson for senior service, with the likes of Luke Shaw, Rahaeem Sterling, John Stones and Saido Berahino all featuring in the early qualifying games for Southgate.
And with strike pair Harry Kane and Danny Ings becoming the latest Under-21s stars tipped for potential senior call-ups next month, Southgate is hoping that their stellar form continues into the summer.
"Whether we get all of those lads, Roy has said he is happy for them to play for us in the summer," he added.
Watch Gareth Southgate as he's quizzed by a local schoolboy in Middlesbrough
"Clearly, somebody like Harry going as well as he is at the moment, might get a nod [in March].
"Although, we are almost two months away so a lot can change.
"But I know in my mind pretty much who that squad will be and then who the next ones would be in each position so I am quite settled on that."
The Under-21s are in action again next month, when they head to Prague for a game with Czech Republic on Friday 27 March before they face Germany at Middlesbrough’s Riverside Stadium on Monday 30 March. Click here for tickets.