Sharif, who was ousted in Musharraf's 1999 coup, told a news conference in London that he will return because Pakistan "needs" him.
Saudi Arabia says it hopes Sharif will honor an accord with Riyadh to stay out of Pakistan for a decade. Sharif went into exile in Saudi Arabia after he was toppled in the coup and convicted of hijacking and terrorism.
In Islamabad today, Sharif's party said authorities arrested more than 2,000 of his supporters ahead of Sharif's return. Local officials said 250 "troublemakers" had been detained.