Diaz completes rapid turnaround for Liverpool in styleSep 21
Southgate has been under heavy pressure to select the Leicester City playmaker.
Maddison has been in excellent form this season, scoring six goals and contributing four assists, yet there were doubts over whether he would be picked for England.
However, in a surprise late decision, Southgate has opted to include the 25-year-old as one of eight forwards.
Maddison has one cap at international level and has made no secret of his desire to feature more prominently for England.
Elsewhere Newcastle striker Callum Wilson has been rewarded for his fine form with an England recall, three years on from his last call-up.
Wilson has scored six goals in 10 appearances so far this season to help Newcastle to third in the table with one matchweek left until the mid-season break.
Wilson's role is likely to be back-up for Harry Kane, but he will be a fine option from the bench should England need a goal.
The striker's inclusion comes at the expense of Brentford striker Ivan Toney, who will watch the World Cup from home.
After receiving his first call-up in September, Toney seemed to be in line for a place in Southgate's plans.
His eight goals in the Premier League saw him emerge as a leading contender to play second fiddle to Kane, but Wilson's red-hot form means the Newcastle striker gets the nod over the Brentford marksman.
At the back, the most eye-catching inclusion is Arsenal defender Ben White.
White was a surprise omission from the most recent England squad but his performances for table-topping Arsenal have earned him a recall in time for the World Cup.
White has been one of the most impressive defenders in the Premier League this season, operating primarily as a right-back for Mikel Arteta's side.
With England short of options at full-back, he provides Southgate with a versatile and athletic defensive option, capable of playing as a right-back, centre-back or even as a defensive midfielder.
The 25-year-old has four caps to his name and will expect to add to that tally in Qatar, where he will be a strong contender to start on the right of Southgate's back three.
Players to miss out include AC Milan defender Fikayo Tomori, Marc Guehi, Tammy Abraham, Jarrod Bowen, James Ward-Prowse, Joe Gomez and Tyrone Mings.
Despite making a substitute appearance in the final of Euro 2020, Jadon Sancho has paid the price for Manchester United's inconsistent start to the season and misses out on a place on the plane.
The decision to include injured Man City duo Kyle Walker and Kalvin Phillips is a gamble considering given how long the pair have been sidelined with injuries.
Chelsea full-backs Reece James and Ben Chilwell miss out through injury.
The Three Lions qualified comfortably but have since endured a poor run of form and suffered the embarrassment of relegation from their Nations League group.
Southgate will be hoping England pull themselves out of their slump as the countdown to England's World Cup opener against Iran begins.
Who is in the England squad?
Jordan Pickford (Everton) Nick Pope (Newcastle), Aaron Ramsdale (Arsenal).
Defenders: Trent Alexander-Arnold (Liverpool), Conor Coady (on loan at Everton from Wolves), Eric Dier (Tottenham), Harry Maguire (Manchester United), Luke Shaw (Manchester United), John Stones (Manchester City), Kieran Trippier (Newcastle), Kyle Walker (Manchester City) Ben White (Arsenal).
Jude Bellingham (Borussia Dortmund), Mason Mount (Chelsea), Kalvin Phillips (Manchester City), Declan Rice (West Ham), Jordan Henderson (Liverpool), Conor Gallagher (Chelsea).
Marcus Rashford (Man United), Phil Foden (Manchester City), Jack Grealish (Manchester City), Harry Kane (Tottenham), Bukayo Saka (Arsenal), Raheem Sterling (Chelsea), Callum Wilson (Newcastle), James Maddison (Leicester City).
England’s group stage fixtures
England vs Iran: 1pm, Monday 21 November (Khalifa International Stadium, Al Rayyan)
England vs United States: 7pm, Friday 25 November (Al Bayt Stadium, Al Khor)
Wales vs England: 7pm, Tuesday 29 November (Ahmad bin Ali Stadium, Al Rayyan)