McClaren's U-turn on the Real Madrid midfielder was his biggest decision since taking over from Sven Goran-Eriksson after dropping Beckham following last year's World Cup.
"I have looked at David since the New Year and watched him very closely," McClaren told reporters. "He looks very fit, the fittest I have seen him for a long, long time.
"It's my decision and I stand or fall by that. I listen to the advice. (Assistant coach) Terry Venables has been in this position and knows it and understands it.
"Everyone is around the table but ultimately I've got to make that decision," he added ahead of Friday's friendly against Brazil and the Euro 2008 qualifier in Estonia on June 6.
"The only thing that will help me to get the support of the fans is to win football matches," said McClaren. "That's why I brought David Beckham back.
"Not for the fans, not for the media, not for anybody, but the squad, the team, England, to get us winning football matches. That's all it is. It's all about on the pitch. That's my job."
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Beckham has earned rave reviews over the last few months and has helped give Real a chance of winning the La Liga title since they are level with champions Barcelona on points at the top.
McClaren said he had not been swayed by public opinion and added that Beckham's impressive form was the sole reason why he has been recalled for a must-win game in Estonia next week.
England need a lift following disappointing displays against Israel and Andorra in their last two qualifiers which has left them fighting to reach the finals in Austria and Switzerland.
They are fourth in Group E two points behind leaders Croatia, who have a game in hand, and level on 11 points with Israel and Russia. Estonia have yet to pick up a point.
McClaren is confident Beckham's return can help lift the whole squad and can already sense the impact he has had as the players prepare to face Brazil at the new Wembley.
"Whether it is to prove me wrong or whatever, it is probably to prove something to himself that he still wants to play at this level. He can. He has proved that. This is a big game.
"I know David well enough and he just wants to play. We must deliver now, that's the key thing. There's a good hunger among the players, despite having a hard season.
"They have that look of resolve in their eye that 'We've got to do the business now'."