As initially reported by L'Equipe, and since confirmed by ESPN FC, 29-year-old Herrera arrives at Parc des Princes on a free transfer from Manchester United in a deal negotiated by former sporting director Antero Henrique, which had been suspected at Old Trafford for some time.
Sarabia, as first reported by Paris United, was negotiated in part by Henrique and finished by successor Leonardo, with ESPN FC sources indicating that the 27-year-old will cost PSG no more than €22 million due to a relatively low minimum fee release clause.
As reported by RMC Sport and since verified by ESPN FC, the Spanish pair have since undergone their medicals in Paris and the French champions are ready to make their joint arrival official on top of launching their new home kit.
Herrera is likely to replace Adrien Rabiot in the PSG midfield with the France international likely leaving.
Leonardo is also looking into moving January arrival Leandro Paredes on already.
Sarabia will give coach Thomas Tuchel options in the attacking third after the sale of Moussa Diaby to Bayer Leverkusen and both will put pen to paper on lengthy contracts.
Regarding Rabiot's future amid links with a free transfer switch to Juventus, his mother and agent Veronique admitted contact with Leonardo to RTL but denied the offer of a contract extension.
"I have read absolutely everything, including that Adrien had a meeting with Leonardo that he did not show up to," she said.
"There were also claims that I received an offer of a contract extension from Leonardo and rejected it.
"This is absolutely wrong -- there has not been the slightest discussion between Leonardo and I.
"I have had Leonardo on the phone since his return and we greeted each other with courtesy. He is an intelligent man. There was no offer and there will not be one. It was not even to gauge the temperature."
On the links with Juventus, Rabiot's mother was keeping the pair's cards hidden.
"You know, in football, we are very superstitious," she said. "It is better to say as little as possible until something is done."
ESPN FC's Eduardo Fernandez Abascal contributed towards this report.