The controversial right-hander made the first triple century of his career to offer a timely reminder of his talents to new England cricket director Andrew Strauss.
But after meeting with Strauss in the evening Pietersen was told he will not be recalled to the England side.
Pietersen, sacked by England last year, batted for over seven hours against Leicestershire at The Oval.
"I'm desperate to play for England again. That's what I want to do. It's not just numbers, but how important the timing is," the South-African born batsman told Sky Sports.
"The pressure I was under this morning ... that's one of the best innings I've ever played.
"I knew that I basically needed to answer and question with runs and goodness: 326 is a pretty good argument."
It was Pietersen's 50th first-class ton and his first county championship hundred for nearly two years. He has faced 373 balls, hitting 34 fours and 14 sixes.
Pietersen was sacked by England in February 2014 following the team's 5-0 Ashes defeat in Australia after being accused of being a divisive character in the squad.
But the 34-year-old said the only thing that mattered was what the players produced on the field.
"Personal differences between personalities have nothing to do with what the public wants. The public wants to see England cricket winning. I feel I can add to the England team doing well this summer," he said.
Pietersen met with former England captain Strauss, who has had his own problems with the controversial right-hander, and ECB chief executive Tom Harrison on Monday evening.
England's leading run scorer in all forms of international cricket was dropped after sending text messages about his skipper Strauss to South Africa players during a test series in 2012.
Strauss had to apologise last year after using an offensive term to describe Pietersen while working as a television commentator. He had not been aware his comments could be heard live on air.
Strauss, who will face the media for the first time in his new role at Lord's on Tuesday, must appoint a new England coach following the dismissal of Peter Moores on Saturday with the first Ashes test against Australia starting on July 8.
Pietersen may have been encouraged by the departure of Moores, with whom he had a fractious relationship, but he knew he also had bridges to build with Strauss.
Moores was fired in 2009 after his first spell as England coach following a fall-out with then captain Pietersen.
(Editing by Ken Ferris and Pritha Sarkar)
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