Ford’s shares were up about 1.5 percent in midday trading on Monday.
The board’s decision to change management was made on Friday, eight days after Mr. Fields had been sharply criticized during the company’s annual shareholders’ meeting for Ford’s deteriorating financial results.
William C. Ford Jr., the company’s chairman, said in an interview that he had subsequently met with Mr. Fields and that they had “decided mutually” that Mr. Fields would retire after 28 years with the company.
That cleared the way for the board to offer the top job to Mr. Hackett, 62, a longtime chief of the office furniture giant Steelcase and a former Ford director, who joined the company’s operational ranks last year as head of its “smart mobility” operation, which includes driverless technology.
“Extraordinary times require transformational leadership, and that’s what Jim has been his entire career,” said Mr. Ford, whose great-grandfather was Henry Ford, the company’s founder.
Mr. Hackett said the board had given him a free hand to transform the nation’s No. 2 automaker, including seeking alliances with Silicon Valley firms, changing its product lineup, and divesting itself of unprofitable global operations.
“I’ve got all the opportunity to make the decisions we need and a great team to help me get there,” Mr. Hackett said in an interview.
Mr. Fields, 56, could not be reached for comment. As recently as last week, he had been trying to strengthen Ford’s bottom line by cutting 1,400 salaried jobs. But, unable to reverse the stock decline, he ran out of time to carry out his strategy to cut costs and expand Ford’s lineup of trucks and sport utility vehicles, while also investing in autonomous and electric vehicles.
Despite spending heavily on self-driving research, Ford was struggling to keep pace with larger automakers such as General Motors and tech giants like Google, both of which have been testing self-driving vehicles. Ford is promising to have a fully autonomous vehicle on the road by 2021.
The upstart vehicle maker Tesla — which recently surpassed G.M. and Ford in market capitalization — is bringing its first mass-market electric model to market this year.
At the annual meeting on May 11, Mr. Fields said Ford was capable of staying competitive in the current market for new vehicles, while also “keeping one foot in the future” of an industry heading toward autonomous, battery-powered cars.
Yet Ford is showing troubling signs of decline. Profit in the first quarter dropped more than 30 percent from a year earlier, and the company’s market share in the United States fell slightly.
And with auto sales in the United States cooling off after two record years, Ford faces a tough balancing act if it is to maintain strong results in North America while investing in projects for the future.
Mr. Fields was also at the forefront of an abortive plan to build a $1.6 billion assembly plant in Mexico for small cars. The project was abandoned early this year as sales stalled and President Trump’s election brought pressure on Ford to make more vehicles in the United States.
Mr. Hackett said at the news conference that he endorsed the decision to abandon the Mexico plant, but added, “We made that decision not for political reasons but for business decisions, and they are still sound today.”
While praising Mr. Fields’s contribution to the company, Mr. Ford said the automaker needed to move faster on new initiatives and to better explain its long-term strategy.
“Clearly our messaging needs to be crisper going forward,” he said, adding that overall operations also needed to improve drastically.
“We have to re-energize our business, including sharpening some of our execution,” Mr. Ford said. “Some of the areas of our business haven’t been running as smoothly as they should.”
So far this year, Ford has had a number of safety recalls that have raised red flags about its overall vehicle quality. The company has also experienced a deep decline in the sale of small and midsize cars, leading some Wall Street analysts to suggest that it drop unprofitable models from its portfolio.
Mr. Hackett said that while he wanted to change Ford’s culture to encourage and support innovation, he would also push the organization to fix current problems in the marketplace.
Ford’s car sales are down 25 percent this year — far more than the overall industry decline in the car segment — and it is making little, if any, money on the cars it does sell.
“There are categories of cars that need to hit margin targets,” he said, adding that he had been given “no restrictions” on how to improve earnings.
Mr. Ford acknowledged that there had been some clashes between Mr. Fields and other executives about strategy and how the company might do things differently. But he discounted the impact of personal relationships on the decision to replace Mr. Fields. “That didn’t play into a big way what we are looking at today,” he said. “You can always find those issues. That’s just part of being in business.”
The personnel changes at the company extend beyond the departure of Mr. Fields and the ascension of Mr. Hackett.
Joseph R. Hinrichs, who leads Ford’s crucial Americas division, will expand his role to become executive vice president for global operations. James D. Farley Jr., who runs the European unit, has been appointed to oversee worldwide sales and marketing. And the chief technical officer, Marcy Klevorn, will take over Mr. Hackett’s duties as chief of mobility initiatives.
In a related move, Mark Truby, who previously led the company’s communications teams in Asia and Europe, will immediately take over as its communications chief. He succeeds Raymond F. Day.