Walcott, 20, has established himself in Fabio Capello's seniors but will also play for Pearce's side in the European Under-21 Championships in Sweden, with the opening clash on Monday against Finland.
Arsenal manager Arsene Wenger is strongly opposed to Walcott playing for both teams but Walcott himself wants to travel after missing the 2007 tournament through injury.
Walcott insists he feels fresh after missing four months of the season with a dislocated shoulder - an injury he picked up while on international duty.
"The one thing I would say from my experience as a player, you never know when that injury is going to come," Pearce said. "You never know when you are going to be out for six months, a year or however long.
"If I was giving advice to any player, I would say play as many
matches as you can and if you are selected for your national team play as many matches as you can.
"I did. I'm speaking from experience, not speaking as someone who picked and chose my games.
"You turn up whether you are injured or not. It's a great honour to play for your country because you bet your bottom dollar that when you are 35 or 40 you cannot do it any more.
"Coupled with the fact that he missed four months of the season through injury and missed the last tournament through injury as well, I think we had a valid case."
Despite the start of the Under-21 finals being days away, Pearce does not want Capello to rest Walcott against minnows Andorra in the World Cup qualifier at Wembley tomorrow.
"There will be no consideration about resting," Pearce said.
"Fabio will pick his strongest side, whether Theo is coming to meet us two days later or not is irrelevant.
"If he deems they need to play 90 minutes then so be it. We need to beat Andorra as a nation, that is the most important thing now."
Pearce spoke with Wenger on the phone about Walcott's inclusion and revealed that the topic was not brought up when he met the Frenchman face to face the following day.
"We disagreed but were civil," Pearce said. "I saw him the following night at an Arsenal match and we shook hands. We didn't speak about our conversation the day before.
"I can't speak for Arsene but I have total respect and he has supported us fantastically well bearing in mind we have Kieran Gibbs with us as well.
"The most important driver in the whole conversation was the fact that Theo wants to be part of the squad."