Stephen D. Bechtel Jr., who led his family’s engineering and construction firm for three decades, expanding an already sprawling operation into an international behemoth with projects including the Channel Tunnel linking Britain and France and Jubail Industrial City in Saudi Arabia, died March 15 at his home in San Francisco. He was 95.

Bechtel announced his death but did not cite a cause. Long based in San Francisco, the company officially moved its headquarters to Reston, Va., in 2018. At the time, The Washington Post reported that Bechtel was the eighth-largest recipient of federal contract funds, receiving $5.5 billion from the Defense Department, the Energy Department and other U.S. government agencies the previous year.

Mr. Bechtel represented the third generation at the helm of his family’s company, which was born in 1898 when his grandfather, Warren Bechtel, hired out mules to build railroad tracks in what was then the Oklahoma Territory.

The construction of those railways led to work on pipelines, dams and roadways. Under the leadership of Mr. Bechtel’s father, Stephen D. Bechtel, the company took on such projects as the construction of the Hoover Dam — a monumental public work erected during the Depression by a consortium of builders — and the Bay Bridge linking San Francisco and Oakland, Calif.

Fortune magazine described the elder Bechtel as “the boldest and maybe the biggest builder in the world” and ranked him alongside such industrialists as Henry Ford of Ford Motor Co., John D. Rockefeller of Standard Oil Co. and steel magnate Andrew Carnegie.

Mr. Bechtel joined the company as a field engineer in 1948, took over from his father in 1960 and grew the company further. Sales increased 11-fold under his leadership, according to Bechtel, as the firm pursued projects worth tens of millions of dollars on nearly every continent. Among them was the construction of San Francisco’s Bay Area Rapid Transit system (BART), nuclear power plants across the United States, North Sea oil and gas platforms, and King Khalid International Airport in Saudi Arabia.

Jubail Industrial City, located in eastern Saudi Arabia on the Persian Gulf, has been described as one of the largest civil engineering undertakings of the modern era — “a city built from the sand up,” according to the Bechtel company, and one that grew from “the deserted suburbs of an ancient fishing and pearling village” into a “major industrial complex with harbor and port facilities.”

In the 1970s, Bechtel worked on the construction of Washington’s Metrorail transit system; more recently, it has been a principal contractor on the construction of Metro’s Silver Line in Northern Virginia.

Executives at Bechtel, which was privately held, generally maintained a low profile. The company leadership found itself uncharacteristically in the news in the early 1980s, when its president, George P. Shultz, a former U.S. secretary of labor and the treasury, left to become secretary of state under President Ronald Reagan. Caspar W. Weinberger, the company’s general counsel and a former secretary of health, education and welfare, departed to become defense secretary.

Around that time, Richard Helms, a former director of the Central Intelligence Agency and ambassador to Iran, worked for the company as a consultant.

Associations such as those made Bechtel one of many companies whose leadership seemed to bridge the government and contracting worlds, although Mr. Bechtel told The Post in 1985 that “our people are under orders they can’t go to Shultz or Weinberger on anything, anything affecting Bechtel business, client business or U.S. government affairs.”

Bechtel was the subject of the 1988 book “Friends in High Places: The Bechtel Story — The Most Secret Corporation and How It Engineered the World” by journalist Laton McCartney, detailing claims including the allegation that the company had participated in CIA operations in the Middle East.

The company denied any involvement with the intelligence agency and described the book as a work of “fabrication, falsehood, and innuendo woven into an inaccurate account of Bechtel’s history.”

Mr. Bechtel led the company through a difficult period in the 1980s, when a drop in oil prices sharply curtailed the availability of construction projects in the Middle East, before his retirement in 1990. The next year, President George H.W. Bush awarded him the National Medal of Technology and Innovation “for his outstanding leadership in the engineering profession.”

Stephen Davison Bechtel Jr. was born in Oakland on May 10, 1925. A New York Times obituary for his mother, Laura Peart Bechtel, described her as an “active partner and adviser” in the family business.

Mr. Bechtel was an Eagle Scout — years later donating $50 million for the construction of the Summit Bechtel Reserve scouting center in West Virginia, the largest donation in the history of the Boy Scouts — and joined the Marine Corps around the time of his high school graduation.

He received a bachelor’s degree in civil engineering from Purdue University in 1946 and a master of business administration degree from Stanford University in 1948.

He later recalled recognizing “some disadvantages of going into the family business,” according to Investor’s Business Daily, as opposed to launching a new career of his own. But Mr. Bechtel agreed to sign on after an around-the-world cruise with his new wife, courtesy of his father, that allowed him to see the reach of his family’s operations. His first assignment took him to Texas, where he worked as an engineer during the day and drove a transport truck at night.

After retiring in 1990, Mr. Bechtel was succeeded by his son, Riley Bechtel. A grandson, Brendan P. Bechtel, succeed him in 2016. In recent years, the U.S. government has contracted with Bechtel for reconstruction work in Iraq and Afghanistan following the wars in those countries.

In addition to his work at Bechtel, Mr. Bechtel was chief executive of Fremont Group, a real estate development and management concern with a venture capital arm that was an early backer of the Starbucks coffee chain. Mr. Bechtel retired from that position in 1995. He was also a director of companies including IBM and General Motors.

In 1946, he married Elizabeth Mead Hogan. Besides his wife, survivors include five children, Riley Bechtel, Gary Bechtel, Shana Johnstone, Lauren Dachs and Nonie Ramsey; 16 grandchildren; and 30 great-grandchildren.

Forbes estimates Mr. Bechtel’s wealth at $2.9 billion. According to the company, his foundations have distributed more than $1 billion in grants over the years, particularly in the area of science, technology, engineering and math (STEM) education.