The South Africa-born number four missed the recent Test series against New Zealand with a knee injury that required surgery.
There had been doubts regarding his fitness for the upcoming Ashes, but he has recovered in time and has been included in the 13-man squad for the first clash of the five-match series with Australia at Trent Bridge on Wednesday.
With Pietersen back involved, Butcher believes that it will bring better performances out of the rest of the squad.
"KP's mere presence in the order makes the rest of our batters 10% better/more confident. Vital player," he wrote on Twitter.
England have won three of the four Ashes series that Pietersen has featured in.