The striker is not one of the 23 players named by Roy Hodgson for the tournament, although he was selected for the standby list of seven the England manager will call upon if needed.
The 31-year-old, capped 55 times since making his England debut in 2004, moved from Tottenham to Major League Soccer outfit Toronto FC in January but was part of the national side as recently as last November when he appeared off the bench against Chile.
But with Hodgson opting for Wayne Rooney, Daniel Sturridge, Danny Welbeck and Rickie Lambert as his four strikers, Defoe has been omitted from a World Cup squad for the second time, having also missed out in 2006.
"It's hard even to find words to describe how I am feeling," Defoe declared. "I felt I had done enough. I feel sharper than ever and I have been on form and scored goals."
Defoe did appear for England at the 2010 World Cup in South Africa, scoring the only goal of the game as Fabio Capello's side edged past Slovenia in their final group game.
Following the death of his father during Euro 2012, Defoe flew home but later re-joined the England squad for the rest of the tournament.
Reflecting on his omission for Brazil, the former West Ham and Portsmouth player admitted, "To miss out, I feel devastated. I didn't really feel I had to sell myself to the manager.
"I had a situation at the 2012 Euros where I lost my dad and I had a decision to make. But I chose to go back out to Poland and Ukraine because I know how important it is to play for your country."
Meanwhile, Hodgson has backed his youthful squad to make an impact in Brazil.
"These youngsters have imposed themselves upon me and my thinking because they've been so effective and successful for their clubs.," said Hodgson.
"A lot of water has gone under the bridge since we qualified back in October and you can't ignore what these players have been doing on a week-to-week basis.
"There are an awful lot of caps in this 23 so we shouldn't get too hung on the amount of youngsters. But they deserve to be in there. I'm not taking anyone just for the experience.
"I believe the squad can win the World Cup. Otherwise what's the point in taking part? But if we're going to win then we have to prepare and play very well.
"This group has got a lot of talent, we all know it, but they have got to show their talent otherwise all the belief, optimism and words count for nothing.
"There is a mood of positivity around us and we'll work and feed off that. Whether it takes us to the World Cup final who knows but we'll do our best."