The arrival of Mertesacker, who agreed a four-year deal in a reported nine million pound transfer from Werder Bremen on Wednesday, will bolster the team's shaky defence - especially since he is in the mold of rugged Arsenal great Tony Adams rather than his light-footed successors under coach Arsene Wenger.
"I don't think my transfer was [Wayne] Rooney's fault," Mertesacker told reporters referring to the United striker's hat-trick on Sunday which helped condemn Arsenal to their heaviest league defeat since 1927.
It also raised further questions about Wenger's philosophy of evolving teams rather than making the kind of marquee signings that have transformed Manchester City into title contenders.
"I don't' think that [the defeat by United] was the reason, I want to believe they [Arsenal officials] were monitoring me for quite some time. For me a childhood dream comes true," he added.
"There is such incredible potential and we will get out of the position the team is currently in. Arsenal have this ability... to play good football, and to have Wenger on top of that as coach is unbelievable.
"I wanted this for such a long time. It is a challenging task which I will tackle because I will also develop further as a player."
Germany coach Joachim Low said his defender had made the right move.
"This is a very good step and I am happy for him," Low said. "Per will develop immensely at Arsenal. They stress that you have to play with two touches, play it quicker out of defence," said Low.
The 26-year-old was one of several late signings by Arsenal including Spanish midfielder Mikel Arteta and Israel midfielder Yossi Benayoun on a season-long loan from Chelsea.
