Zimbabwe's veteran opposition leader, Morgan Tsvangirai, has been sworn-in as prime minister, setting the stage for the installation of a power-sharing government on Friday.  The former labor leader delivered a major electoral defeat to President Robert Mugabe in elections last March.

Zimbabwe's new Prime Minister Morgan Tsvangirai defeated President Robert Mugabe in elections last March, but withdrew from the runoff vote citing a campaign of violence against his supporters by Mr. Mugabe's ZANU-PF party.

The political standoff that followed led to months of negotiations and the swearing-in of Mr. Tsvangirai as prime minister under a power-sharing agreement.

"I, Morgan Richard Tsvangirai, do swear that I will be faithful and bear true allegiance to Zimbabwe and observe the laws of Zimbabwe, so help me God," he said.

Until he agreed to join the unity government two weeks ago, the political career of the former mine worker and trade-union leader had been marked by an unwavering criticism of the 29-year rule of the hero of Zimbabwe's liberation, as in these remarks last year.

"Mugabe is now not only the president of the country," said Mr. Tsvangirai. "He is the institution that has run our country for the last 30 years.  And look at the results: unprecedented levels of decay and misrule and repression.  So he should be accountable."

Morgan Tsvangirai was born in 1952 in the Gutu area southeast of Harare in what was then called Southern Rhodesia.  The eldest son of a bricklayer, he was obliged to leave school early in order to help support the family with nine children.

In 1974, he began working in a nickel mine in northeastern Zimbabwe and during the next 10 years rose to become foreman.  In 1989 he was elected Secretary-General of Zimbabwe's Congress of Trade Unions.

In 1997 and 1998, Mr. Tsvangirai led a series of crippling strikes against high taxes, which led the trade confederation to split from ZANU-PF and eventually to the formation of the MDC in 1999.

The MDC won almost one-half of the seats in the parliamentary elections the following year, despite a campaign of violence that left about 30 supporters dead.

Mr. Tsvangirai challenged Mr. Mugabe in the presidential elections of 2002, which were also marred by extensive violence and voting irregularities, and lost by 400,000 votes.

The MDC split over Mr. Tsvangirai's decision to boycott the parliamentary elections of 2005.  A splinter faction headed by Arthur Mutambara, who became deputy prime minister Wednesday, participated, but the split was a major factor in the overwhelming victory by the ZANU-PF party.

Mr. Tsvangirai has been criticized for authoritarianism.  In 2001, his supporters attacked party dissidents and two years ago he installed his candidate for head of the party's women's wing in what critics said was an undemocratic fashion. 

The veteran opposition leader says he has survived four assassination attempts.  One of them, an attempt in 1997 to throw him out of the window of his 10th-floor office, reportedly was only thwarted by the arrival of his secretary.  He was also charged with treason on three occasions, but the cases were dismissed.

Two years ago he and several-dozen opposition leaders were hospitalized after being beaten and jailed for staging a protest that had been banned by the government.

The government-owned Herald newspaper, which has been one of Mr. Tsvangirai's fiercest critics, Wednesday praised his entry into the government and urged the various parties to declare a national cease-fire in order to revive the country's ailing economy.