"The dreams and hopes of all the people of our country must be fulfilled," Zuma promised. "There is no place for complacency, no place for cynicism, no place for excuses."
South Africa's fourth president since apartheid ended 15 years ago is no stranger to struggle. Zuma, 67, is a former guerrilla fighter and intelligence chief of the African National Congress who has since survived corruption and sex scandals and an internal power struggle within his party.
The ANC handily won last month's parliamentary elections and Zuma was elected president by parliament on Wednesday.
Many impoverished black South Africans believe Zuma's personal battles and eventual triumph give him special insight into their own struggles and aspirations.
Zuma urged South Africans on Saturday to ensure "that the struggles and sacrifices of our people over many decades shall not be in vain. Instead, they shall inspire us to complete the task for which so much blood was shed and so much hardship endured."
Zuma now leads a country where at least a quarter of the work force is unemployed and 1,000 people die of AIDS every day.
He is promising to speed up delivery of houses, clinics, schools, running water and electricity. But he also has acknowledged the difficulties amid a global economic meltdown. According to government figures this week, 208,000 jobs were lost between the last quarter of 2008 and the first quarter of 2009.
On Saturday, he acknowledged the "difficult economic times" and that "we are beginning to feel the pinch." But he said "the foundations of our economy are strong and we need to continue to build on them" through more hard work than ever.
A fleet of helicopters suspending South Africa's red, green and blue flags flew over Saturday's ceremony. Cannons boomed, a military brass band broke into the anthem "God Bless Africa." Zuma took a military salute as fighter jets streaming colored smoke zoomed above.
Tens of thousands had broken into spontaneous song when Zuma arrived, beaming, accompanied by his senior wife, Sizakele Khumalo. Zuma's unabashed polygamy has raised questions about which of his three current wives may act as first lady. On Saturday, all three were reported present but only Khumalo accompanied him to the stage, where Zuma dropped down onto his knees before Mandela in a traditional sign of respect.
Sydney Mokoena, a 48-year-old Pretoria high school teacher, roused his 10-year-old daughter, Thula, at 4:30 a.m. to get to the lawns early. He said he admired Zuma for the calm he showed during his legal battles over corruption allegations that have now been dropped and a 2006 rape trial that ended with acquittal.
Mokoena also said that while Zuma may not have had much formal education, his leadership of the ANC's intelligence wing during the anti-apartheid struggle was proof he was smart enough to be president.
Zuma will be "a dynamic and vibrant president," Mokoena said. "That's what South Africa needs. He's down to earth and he'll listen."