Saleh promised "real partnership" with the opposition in implementing the Gulf- and UN-brokered agreement, and King Abdullah of Saudi Arabia, who hosted the signing ceremony at his Al-Yamama palace in Riyadh, hailed a "new page" for the impoverished neighbouring country.
But thousands of demonstrators again to took the streets of the Yemeni capital Sanaa to protest against the deal's promise of immunity from prosecution for both Saleh and his family.
A spokesman said they rejected the agreement signed in Riyadh. The organising committee of youth protesters said the Gulf-brokered deal "does not concern" protesters, Walid al-Amari told AFP.
It called for new demonstrations to demand his immediate departure. Under the agreement, which Saleh had stalled for months in defiance of intense domestic and international pressure, the veteran leader will hand his powers to Vice President Abdrabuh Mansur Hadi but remain honorary president for 90 days.
Saleh has repeatedly backed out of signing the deal brokered by Yemen's wealthy Gulf neighbours since the parliamentary opposition inked it back in April.
During his months of prevarication, deadly clashes between loyalist and dissident troops had riven the capital, while militants, some linked to Al-Qaeda, took advantage of the decline of central government control in the provinces to set up base.