Zanardi, the Italian who earlier this month secured a second consecutive Cart championship, has long been expected to relaunch his Formula One career and replace Jacques Villeneuve, the reigning world champion bound for the new BAR team.
The way was cleared to sign 23-year-old Schumacher when Jordan agreed to release him in an out-of-court settlement and take his fellow German, Heinz-Harald Frentzen, from Williams in his place.
In announcing this line-up, Williams refer only to next season, but it is understood both drivers have built-in options that could keep them with the team in the long-term.
Many observers feel that Williams, even by their own standards, have gone out on a limb. Neither driver has won a grand prix or acquired substantial experience in this championship. It remains to be seen whether they can harness inherent speed and aggression to the benefit of themselves and the team.
However, Williams were left with few options as they face the prospect of a transitional period. Their car will be powered by the Mecachrome engine for another year until they join forces with BMW, and instant success with new partners is unlikely.
Williams were unable to compete for Michael Schumacher, Mika Hakkinen or David Coulthard, and Villeneuve chose to leave. Villeneuve's achievements in Formula One encouraged them to believe in Zanardi, while the younger Schumacher offers promise and an obvious link with BMW.
"We believe we have a very strong line-up for the 1999 season," the team's managing director, Frank Williams, said. "Both drivers will bring their own special qualities. We are excited at the prospect of welcoming a second transatlantic champion to the team in Alex, and Ralf is showing great potential. We believe he has a remarkable career ahead of him. They should be good competition for each other."
Zanardi made his Formula One debut with Jordan in 1991. But 25 races with three teams over four seasons yielded only one point. He decided to look across the Atlantic, and has gained 14 victories, 25 podium finishes and two titles in the past three years.
He had lucrative offers as well as the virtual guarantee of continued success in North America, but yearned to return to Europe and prove himself.
"I feel I got the most of my three years in Cart and now it's time to turn a page in my career," he said. "Driving for Williams will provide me with a fantastic technical package."
Schumacher, who was advised to join Williams by his brother, Michael, came into Formula One at the beginning of last season. He is ninth in this year's championship, following second and third places in the last two grands prix with Jordan.