The former England U21 boss initially rejected the opportunity to replace Billy Davies at the City Ground due to family reasons and media commitments at this summer's World Cup finals in Brazil.
But after a further approach from Al-Hasawi, who outlined his intention to 'wait for the right man', Pearce had no hesitation in accepting the post from July 1.
"I wouldn't call it a u-turn. We had discussions last week and I was very impressed with the owner," said Pearce, who made 532 appearances for the club between 1985-1997, the last six months as a caretaker manager.
"At the time I suggested I had so much on from a personal nature and commercial aspects leading into the summer and including the World Cup as well. It probably wasn't the right time.
"Fawaz came back to me and said: 'look, would you be willing to take the job in the summer?' and I jumped at the opportunity.
"It was a difficult decision to turn round last week and put my personal reasons forward. But everything seems right. It gives me the opportunity to pre-plan for the summer and I've just signed a contract that starts in the first of July."
Pearce insists he has no worries over any interference from Al-Hasawi, and he welcomes everyone at Forest getting involved in taking the club towards the Premier League.
"The one thing that I was very impressed with, the chairman wants to take an interest in the football club and that really impresses me," he said.
"I want the whole club to be as one, and I think that has to start with the man who owns the football club and goes right down to every employee. They have to take an interest in this club.
"And in my time and the time before I was at this club the strength of Nottingham Forest was the togetherness of everybody at the club."
And Al-Hasawi insists Pearce will have a free reign in team selection and player recruitment after reports his 'hands-on approach' had scared off a number of potential candidates for the post.
Speaking to Sky Sports News he said: "I am going to keep away now.
"It was the manager who didn't take the job that mentioned this and I don't blame him because I was waiting to pick the right manager.
"And Stuart Pearce is the right manager for Nottingham Forest."