Thomas H. Boggs Jr. is shown in Washington, D.C., in 1979. (Tom Allen/The Washington Post)

Thomas H. Boggs Jr., a Washington lobbyist whose indefatigable networking, finesse for dealmaking and deep-rooted connections to American political life placed him squarely in the epicenter of the city’s power-broker elite, died Sept. 15 at his home in Chevy Chase. He was 73.

The cause was an apparent heart attack, said his sister, broadcast journalist Cokie Roberts.

Few people were as acquainted with the pathways to power and influence as Mr. Boggs, whose father, known as Hale, rose to Democratic majority leader in the U.S. House and whose mother, known as Lindy, served nine terms in Congress. Young “Tommy” Boggs’s first job in Washington was operating the private elevator for then-House Speaker Sam Rayburn, the Texas Democrat.

Socially and professionally, Mr. Boggs knew presidents, Cabinet secretaries and members of Congress — and, sometimes more important, their staffs. He became Washington’s most high-profile legal and political adviser in an elite core of gatekeepers and kingmakers that included Thomas “Tommy the Cork” Corcoran in the 1940s and later Clark M. Clifford. Both were family friends.

Starting in the late 1960s — when lobbying was often a one-man operation or done by a trade association — Mr. Boggs helped transform the profession into a sprawling, multibillion-dollar enterprise that seeks access and then regulatory action across a vast spectrum of public policy goals. He helped pioneer the “revolving door” culture of hiring former members of Congress and others with enough prestige to get the right people on the phone, fast.

Thomas H. Boggs Jr., chairman of the legal and lobbying firm Patton Boggs, is shown in his office in 2012. (Jeffrey MacMillan/For The Washington Post)

Mr. Boggs, who charged upwards of $550 an hour for his time, was often called a “hired gun.” He never seemed to protest. Instead, when one magazine called him “an icon of Washington’s mercenary culture,” he hung the article on his office wall.

His quips, at times, played into the worst popular notions of lobbying — “We pick our clients by taking the first one who comes in the door,” he once said. To another interviewer, he added: “We don’t get paid to be philosophers.”

With a self-awareness and gregarious charisma that even his nemeses among good-government groups found hard to resist, Mr. Boggs spent more than four decades as a heavyweight in Washington influence peddling. He sometimes attended three fundraising events in a single night.

He had a shrewd understanding of how the city operated behind the public view — how to get to people in a position of power and how to win their support, often via large donations. In 1970, he made an unsuccessful run for Congress representing suburban Maryland, an experience that made him even more sympathetic to the needs of political aspirants and survivors.

Whether by virtue of pedigree or a perspective informed by close-up working relationships, he expressed in colorful terms the joy he felt of being in the presence of politicians and their ability to find solutions to serious problems.

“Members of Congress work their panties off,” he once told The Washington Post. “If you took the 535 of them and stacked them up against 535 of the top people who sit around corporate boardrooms, I’d take the congressmen for sheer brainpower any day.”

By his mid-30s, Mr. Boggs had risen to the apogee of influence in the wake of Watergate-era reforms that saw an “explosion and diffusion” of committee oversight and power, said Charles Lewis, an author of books on money in politics and founder of the nonprofit watchdog group the Center for Public Integrity.

Instead of a handful of people who controlled the levers in town, the joke went that when a lobbyist went to Congress, he could say “Hello, Mr. Chairman” and everybody would turn around. (A rite of passage in some Washington circles — especially among those ubiquitous subcommittee chairmen — was an invitation to Mr. Boggs’s farmhouse on Maryland’s Eastern Shore for a weekend of duck hunting and socializing.)

Mr. Boggs’s firm, which became known as Patton Boggs, had a strong tax-legislation division. He developed a client base that included oil, drug, insurance and chemical companies; the communications firm MCI; and even the candymaker Mars.

The firm worked to persuade Congress in 1979 to approve federal loan guarantees of up to $1.5 billion for the bankrupt automaker Chrysler. He also worked for oil and construction companies eager to see the Trans-Alaska Pipeline System come to fruition in the 1970s.

He saw his prospects surge after the 1992 election of Bill Clinton to the presidency. A Patton Boggs partner, Ronald H. Brown, was named Clinton’s commerce secretary. Another Patton Boggs partner, Lanny J. Davis, became a White House special counsel.

The Republicans retook power in both houses of Congress during the 1994 elections, and Mr. Boggs began to take a strong interest in GOP fundraisers. He also diversified his staff to include many lawyers with ties to the Republican Party.

For the Association of Trial Lawyers of America, Patton Boggs worked to scuttle the Clinton-era health-care revisions out of concern over a cap on malpractice claims. For the American Bankers Association, Mr. Boggs helped argue for the repeal of the Glass-Steagall Act, a Depression-era law that prohibited commercial banks from combining with brokerage houses.

The repeal, part of a larger appetite for deregulation in the late 1990s, is often said to have played a significant role in worsening the financial collapse of the late 2000s.

Patton Boggs was on the U.S. Supreme Court brief for GOP candidate George W. Bush during the contested 2000 presidential election. As he explained to the Denver Business Journal, “when the Republicans take over the White House, the business community basically thinks they can get a lot done.”

Patton Boggs also worked for foreign entities, including some that were highly unsavory. They included the Haitian dictator Jean-Claude “Baby Doc” Duvalier and an association of Guatemalan businessmen who in the early 1980s wanted to replenish U.S. military assistance for President Romeo Lucas Garcia, a general accused of human rights abuses. The lobbying firm also represented the Bank of Credit and Commerce International, a financial institution that collapsed amid charges of money laundering and other misdeeds.

Mr. Boggs’s namesake firm was subsumed this summer by the larger law firm Squire Sanders because of declining revenue and high-profile departures of partners, prompted in part by setbacks for the firm in a battle with Chevron.

Patton Boggs had sided with plaintiffs seeking payment from the oil giant over toxic oil waste left behind in Ecuador decades ago. But Chevron had alleged wrongdoing on the part of the plaintiffs and Patton Boggs regarding a $9.5 billion judgment against Chevron in an Ecuador court in 2011. The firm recently settled its dispute with Chevron, paying the oil company $15 million. At his death, Mr. Boggs was chairman emeritus of the newly named Squire Patton Boggs.

Thomas Hale Boggs Jr. was born Sept. 18, 1940, in New Orleans and grew up in Bethesda. His father, who first came to Congress in 1941 to represent Louisiana, died in a plane crash in Alaska in 1972, and his mother, the former Corinne Claiborne, won the special election for her husband’s seat.

After graduating in 1958 from Georgetown Preparatory School, Tommy Boggs received an undergraduate degree from Georgetown University in 1961 and a law degree from Georgetown in 1965.

In 1960, he wed Mary Barbara Denechaud. Besides his wife, of Chevy Chase, and sister, of Bethesda, survivors include three children, Thomas Hale Boggs III of Manhattan Beach, Calif., Elizabeth Boggs Davidsen of Chevy Chase, and Douglas Boggs of Bethesda; and eight grandchildren.

His mother, who served as Clinton’s ambassador to the Vatican, died last year at 97. Another sister, Barbara Boggs Sigmund, died of cancer in 1990 while serving as mayor of Princeton, N.J.

After graduating from law school, Mr. Boggs said, he turned down an offer at a big law firm on the advice of a mentor, the presidential confidant and defense secretary Clark M. Clifford.

He said Clifford advised him to go to a firm that would give him the most grounding in legal basics, and so he joined the staff of a four-member firm co-founded by James R. Patton Jr. He made $12,000 a year.

“My father was disappointed,” Mr. Boggs told The Post in 1983. “He had gone to a great deal of effort to make sure I was interviewed at all the Big Daddy firms in town. We never had much money, and the best he could give me was heritage and opportunity, and here I was not taking advantage of ‘opportunity.’ He said I was stupid.”

Three years later, the law firm became known as Patton, Boggs and Blow, the last for partner George Blow. Neither other namesake partner had the same gusto for publicity, allowing the entrepreneurial Mr. Boggs to fashion its public reputation to his “hired gun” style.

For all his more flamboyant side — the Havana cigars, the duck hunting — he could trace his success as a lobbyist to his old boss in the elevator, Rayburn. The former House speaker told him the greatest skill in lobbying was the ability to listen and know how far to push. “Politics is the art of the possible,” Mr. Boggs said.

Correction: A previous version of this story included an incomplete name for a sister, Barbara Boggs Sigmund. This version has been corrected.