Sancho has made a stunning start to the new season with Borussia Dortmund and is now the leading assist maker in Europe's top five leagues with eight assists, despite having just started two games in all competitions.
Mount has created more chances than any other player in the League Championship and scored for England's under-21 team last month.
Southgate has handed first senior debut call-ups to Mason Mount, Jadon Sancho and most notably James Maddison who has been in phenomenal form for Leicester City so far this campaign.
When asked about the inclusion of the young trio of Mount, Sancho and Maddison, Southgate said: I think it's aligned to what we have done in the last 18 months really.
With Dele Alli and Jesse Lingard injured and Adam Lallana and Ruben Loftus-Cheek making their way back to fitness, Southgate has turned to youth. We have a few injuries in midfield in particular so there was an opportunity there. We think there are some exciting young players that we've been tracking, either through their clubs or our junior teams.
"With the Premier League as it is we have to be creative, inventive and have to look longer term".
"Okay, we've got to think differently about it, be bold in some of our decisions and we'll get some of those right and some we won't get right".
"I think very often we hold youngsters back too much". "He's a player that excites us a lot". He played a year ago on loan at Vitesse [Arnhem] and has had another season of men's football and created more chances than any other player in the league. Jadon has had a similar impact for Dortmund in big matches.
Ross Barkley and Nathaniel Chalobah are also called up.
In addition, Ross Barkley's upturn in fortunes at Chelsea means he is in line to win his first cap since the friendly against Australia in May 2016.
"I must acknowledge the hard work and commitment of my staff and the players over the last two years". Having led the team to fourth place in Russian Federation this summer, Southgate - whose salary is believed to have risen to £3million a year - revealed he had no doubts over wanting to stay.
We'd have no hesitation on playing either of them in the games coming up.
"I am delighted to have the opportunity to lead the national team through the next two major tournaments", said Southgate, whose previous deal was due to expire after the Euro 2020 finals.
"But as always, when you get opportunities within the squad - people have come in, in the past, and done well and they stay in". We try to work in the same way and the benefits from that are clear.