The 29-year old will put pen to paper on a deal that will keep him at the Mestalla until 2017, where he has spent the last four years of his career.
Mathieu was reportedly outlined as one of Tito Vilanova's targets to bring to the Spanish champions this summer, but the Frenchman says he will be staying put.
"Everything has been sorted out, I have the new contract in my hands - I just have to sign it," he told L'Equipe.
"I was waiting to see other propositions, but I have always known I would stay. The World Cup is in one year's time and the French team is on my mind.
"I could not see myself start again from scratch while I feel fine at Valencia where I am considered as an important player."
The defender also confirmed that Barcelona were keen on his signature, but he admitted that he probably would not have been first choice at the Nou Camp.
"Interest from Barcelona? Yes indeed, but I was only fourth or fifth position on their list. I just know their top priority was Thiago Silva," he said.
"I could have waited but I had to be respectful towards Valencia who were waiting for my answer for a while.
"After having talks with the coach, I think I will start the new season in the centre of defence."