The American-English term empty suit designates a person—especially a wealthy, professional or powerful man—perceived as lacking substance, personality, intelligence, ability, etc.

I have discovered that this term:
– originated in the slang of Broadway, the centre of New York City’s theatre and entertainment industry;
– was a derogatory term denoting a wealthy man who, in return for their company, lavished money on showbusiness people and those mixing with them.

The earliest known occurrence of empty suit is from Who’s Who and Ain’t Along Broadway: The way to get with ’em is to train nights, sleep days and avoid fresh-air poisoning, by Gilbert Millstein, published in The New York Times (New York City, New York) of Sunday 31^st December 1950. Gilbert Millstein had “recently returned from a safari through Broadway [during which] he interviewed many natives”. In the following passage, he contrasted two groups: the joiners and the big spenders; the latter were men “with a lot of money” but “completely devoid of personality”, and the term empty suit was applied to the dullest of them:

What differentiates the joiner from everyone else is that he has no visible means of support or, rather, no known occupation. His means of support are the people from whom he can promote a touch and he works at this with a single-minded devotion highly suggestive of the pilot fish nosing around a killer shark. […]
Any time from 2 o’clock on in the afternoon, the joiner really starts to hustle. He shows up at any of the herd’s favorite waterholes, depending on what his appetite is like, cases the place for a familiar face and then “joins.” He takes charge of the table, retails the tiny treasures of fact and fiction he has amassed in the past twenty-four hours and eats. […]
The opposite of the joiner is a species known as the big spender or “the real George” (an adaptation of a Las Vegas gambling term indicating a man with a lot of money), whose tenuous connection with the world of entertainment is that he generally provides it for a shifting entourage of joiners of both sexes.
Exactly what moves him is a difficult thing to assess, but one East Side night club owner has attempted to reduce it to its simplest terms. “He is a character completely devoid of personality,” said the owner unhesitatingly, “who woke up one morning and discovered something—girls [cf. note]. One afternoon, I mean.” […]
[…] In the main, the spender appears to be driven by an overpowering loneliness that sends him into expensive saloons every night to consort with people whom he may or may not know. Two of the more colorless representatives of this group at present are known as “The Empty Suit” and “Harvey With Money.”

The Real George (Big Spender) – detail from an illustration by Carl Rose for Who’s Who and Ain’t Along Broadway – The New York Times (New York City, New York) – 31^st December 1950:

The text in which occurs the second-earliest instance of empty suit that I have found confirms that the term originated in Broadway slang; this text is the column It’s All New York, by George Hamilton Combs Jr., published in several U.S. newspapers on Wednesday 21^st February 1951—for example in the St. Joseph News-Press (St. Joseph, Missouri):

In Broadway lingo, the “Empty Suit” is the fellow who always picks up the checks for his pals. He’s usually a stolid businessman who likes the company of writers and show people.

George Hamilton Combs Jr. defined empty suit again—this time explicitly as a derogatory term—in his column It’s All New York, published in The San Bernardino Daily Sun (San Bernardino, California) of Saturday 7^th April 1951:

Broadway Star
There’s Bob Alda, darkly handsome. Movies to Broadway stardom. […]
And there’s that fast striking carpet manufacturer who likes show people and newsmen. Always wants to treat ’em. They always let him. (Insulting slang term for such fellows: “The Empty Suit.”)

In On Broadway, by the gossip columnist Walter Winchell (1897-1972), published in several U.S. newspapers from Wednesday 12^th December 1951 onwards, empty suit was equated with a tiresome, dull person—the following, for example, is from The Post-Star (Glens Falls, New York) of Thursday 13^th:

Ticket Broker Geo. Solotaire’s description of a bore: “He’s an empty suit!”

Note: cf. How a muder popularised ‘sugar daddy’ in 1923.