The 33-year-old is set to make his 100th Test appearance in Brisbane as England’s leading run-scorer across all formats aims to win his fifth Ashes series.
Pietersen, who captained the tourists for a short spell in 2009, has already been described as one of the world’s best batsmen by Australia opener Shane Watson this week.
And Ashes-winning England bowler Harmison, who was Pietersen’s team-mate during wins in 2005 and 2009, believes the South-African born star is great role model.
“Kevin is the best player ever to wear an England shirt,” Harmison told BBC Sport.
“He’s not the best English player to play for England because he’s not English, he is South African, but he is the best player ever to wear an England shirt.
“He has changed the face of the game and the way people, especially young players coming into the game, view the game.
“English people have to be thankful that somebody like that has come along.
“I think he will set all the records for a short period of time before Alastair Cook beats them a little later after Pietersen retires.”