"This act (disengagement) is essential for Israel. Believe me, the pain I feel with this act is the full realisation that we must do it," Sharon said.
"We cannot hold onto Gaza forever, more than a million Palestinians live there ... crowded in refugee camps, poverty and hotbeds of hatred with no hope on the horizon."
But the Israeli leader also said in his televised speech that it was now up to the Palestinians to clamp down on fighters and stop violence, vowing the "harshest response ever" to any attack by Palestinian militants after the pullout.
"To an outstretched hand we will respond with an olive branch, but to fire we will respond with fire more intense than ever before."
For most of his political career, Sharon had led Jewish settlement expansion in the West Bank and Gaza. As recently as two years ago, he said Israel would not give up even small, isolated Gaza settlements.
"To an outstretched hand we will respond with an olive branch, but to fire we will respond with fire more intense than ever before"
Israeli prime minister
"But the changing reality in the nation, region and world made me change my mind and change my position," Sharon said on Monday.
"We cannot hold Gaza forever. More than a million Palestinians live there, doubling their numbers every generation."
In his brief address, he appealed directly to the settlers. "Your pain and your tears are an inseparable part of this country's history," he said, pledging that "we won't abandon you" after the evacuation.
Sensitivity and patience
Faced with hostility and resistance by many settlers, Sharon instructed the army and police to execute their mission "with sensitivity and patience".
He recognised that his unilateral withdrawal plan had aroused a bitter national debate, but Sharon urged the country to unite. "We are one people, also in times of conflict and argument," he said.
"We are alighting on a new path on which there are not a few dangers. But there also is a ray of light for us all," he said.
"Your pain and your tears are an inseparable part of this country's history ... we won't abandon you"
Sharon addressing settlers
Despite Sharon's call, diehard settlers dug in on Tuesday for the final fight against the pullout as the army readied to forcibly evict hundreds of Jewish residents after a midnight deadline.
Settlers have until midnight (2100 GMT) Tuesday to leave their homes voluntarily or face forcible removal by Israeli forces.
After the presence of all Israelis in Gaza was outlawed Monday, angry and emotional Jewish settlers vowed not to desert their homes as an increasing flow of resigned families trickled out of the territory.