In 2000, nine years after he joined Cargill Inc., David MacLennan felt his career had stalled. He was a top leader in Cargill’s financial business, but he seemed pigeonholed as a finance guy, unable to move up in the company.

So he left, figuring he would never return. This was Cargill after all — the venerable Minnesota agribusiness giant still mostly owned by its founding families. Company leaders were almost always lifers, devotees to the Cargill creed.

“When I said goodbye, I thought this is it, they’re erasing my name off any document I ever wrote — I never existed,” MacLennan joked. More seriously, he said, in Cargill culture, “when the door closes, you’re done.”

But as the culture changed, the company rehired MacLennan in 2002 and put him on a new career path. On Sunday, MacLennan, 54, starts as Cargill’s chief executive, only the ninth in the company’s 148-year history.

He will pilot one of the world’s largest privately held companies, with $137 billion in annual revenue, 142,000 employees and interests in everything from chocolate to road salt — all spread over 67 countries. He takes the helm as the corporate behemoth works to create a more nimble culture.

That means communications barriers in the Cargill bureaucracy must fall. It’s a job that starts at the top, with the CEO either setting a regal tone or creating an atmosphere that invites questioning — without fear of getting slapped down.

“Part of internal transparency is having people come up to you and say “Hey, this is what I think is wrong — do you know about this?” rather than, “Oh boy, there’s the CEO, I better not say anything,” MacLennan said.

MacLennan, Cargill’s chief operating officer, was named CEO in September to succeed Greg Page, who is retiring. Page, who played a key role in bringing MacLennan back to Cargill, will remain as the company’s executive chairman.

MacLennan’s exposure to Cargill started young: His father, Everett, was a grain merchant for the company. Cargill moved his dad from post to post, so the Boston-born MacLennan grew up in Toledo, Buffalo, and Chicago before his family moved to the Twin Cities when he was a teenager.

“Until recently, I never had the same mailing address for more than five years in my whole life, ” MacLennan said, noting that his own postings within Cargill included stints in England and Switzerland.

After graduating from Edina East High School, MacLennan went back to Massachusetts to Amherst College, where he majored in English. During his senior year, he snared an internship at a Chicago trading company, working in the Board of Trade’s wheat pit.

It was a time before computers took over trading, when a tightly packed group of mostly men screamed and yelled out buy and sell orders. “I was hooked,” MacLennan said. “This was fascinating — instantaneous price discovery. The market’s going up, it’s going down. You felt that energy.”

MacLennan took a job at the Chicago firm, Goldberg Securities, after college. He started at the bottom, running orders to and from the trading floor. But the idea was to move into management, and MacLennan did so as he took night classes at the University of Chicago, earning an MBA with a specialty in finance.

“He was a prodigious worker, always the first one in and the last one out, ” said MacLennan’s former boss Dave Goldberg, who’s now retired. “He caught on to the business very well.”

Goldberg sold out to an English firm in the late 1980s. MacLennan stayed on for a while, but eventually sensed his first career plateau. He went home to the Twin Cities one weekend and asked his dad, “Would Cargill ever hire someone like me?” His dad said no.

The answer was rooted in his dad’s own tenure at Cargill, when the firm was more of a traditional grain-­trading house. “He was thinking, ‘You come from the financial world, you have an MBA, and we hire guys to be grain merchants,’ ” MacLennan said.

A changing company

But in the 1970s, Cargill began evolving into the company it is today, moving into such diverse businesses as cocoa, cotton and meat processing. By the late 1980s, Cargill had established its own financial and risk management business. Even MacLennan’s dad eventually came around to the possibilities.

MacLennan was hired in 1991 to work in Cargill Financial’s distressed-assets operation, buying up loans that the U.S. government held after taking over failed banks and savings and loans. He worked his way up, becoming Cargill Financial’s CFO in 1998.

In the same year, veteran Cargill executive Page was commissioned to run the financial business. Talk about a hot seat. The Russian government defaulted in 1998, and Cargill held a lot of Russian debt. The financial group was losing a significant amount of money.

“My first experience with David was, ‘We’re in this foxhole together,’ ” Page said. “And here was this very calm Scotsman,” he said of MacLennan. Cargill Financial pulled out of the crisis intact, and by 2000 MacLennan was looking for opportunities beyond financial markets.

“I talked to various people in senior Cargill and said, ‘Where can I take my career?’ ” MacLennan said. “The basic response I got was, ‘You’re a financial markets guy. We would love to see you continue to lead our financial business, but we’re not going to parachute you into flour milling.’ ”

So, “with a lot of mixed feelings,” MacLennan set off to run Minneapolis-based Piper Jaffray’s fixed-income business. But he never lost touch with compatriots at Cargill, including Page, who in 2000 was named Cargill’s chief operating officer.

MacLennan returned from a vacation in February 2002 to find a voice mail from Page. So began the path back. He was offered a post in Geneva, Switzerland, leading Cargill’s energy trading business. After a few years, MacLennan returned to the Twin Cities to head Cargill’s North American pork and turkey business.

In 2008, Page, who by then had become CEO, named MacLennan as chief financial officer, and three years later he became Cargill’s chief operating officer.

Page’s tenure was marked by continuing global expansion and mostly strong profit growth — with Cargill’s fiscal year 2012 being an exception. Pummeled by weak trading results and reduced profits in key businesses, Cargill had its worst year in about a decade, though still earning $1.2 billion.

Cargill even made a rare mass layoff of about 2,000 employees, 1.5 percent of its global workforce. At about the same time, the company launched an effort to reduce bureaucracy and speed up decisionmaking.

“We have eliminated some committees and some levels of approval,” MacLennan said. “We have made progress, but we are not where we want to be in a world that gets faster by the day.” He saw that firsthand in a trip last year to the company’s soybean crushing operation in Tula, Mexico.

“We [met with] a group of young leaders and I asked them, ‘What frustrates you the most?’ They said ‘We have to get too many signoffs to do stuff.’ I said, ‘You have to challenge that.’ ”

Open discussion

MacLennan acknowledges the potential “cost of candor.” The topic came up at an employee meeting last month at Cargill’s sprawling office in Hopkins. Company leaders need to reduce the cost of candor, MacLennan told women executives from Cargill’s food ingredients division.

MacLennan seemed at ease at the meeting, riffing on everything from genetically engineered foods to global political volatility, noting the Venezuelan government’s seizure of a Cargill rice mill a few years ago — tossing in quips along the way.

Before the meeting, he ran into several Hopkins employees whom he knew from past Cargill posts. One greeted him with his nickname, “D-Mac.” MacLennan said he works at remembering faces and names. It’s part of an attempt to get around another corporate condition that employees everywhere often know too well: invisible leader syndrome.

MacLennan said that being accessible and holding employee meetings like the ones in Hopkins and Mexico help open up the company’s culture. “If you can humanize your leadership, and I don’t mean just me, I think that increases candor.”

To illustrate his point, he told of a “town hall” meeting last month in Shanghai. He loaded his slide projector and started. The first question, from an employee named Larry Lin was “You’re the CEO, so we count on you to be very thorough, but your slides say ‘Singapore town hall.’ ”

MacLennan looked back. Sure enough his slides betrayed an earlier stop on his Asian tour. “I said ‘Larry, you got me, and that’s a good one.’ He felt comfortable raising his hand and saying that,” MacLennan said, “and people felt comfortable enjoying the spirit of it.”