For years, private equity firms have sought to join a special club: managing $1 trillion in assets, a milestone that would put them in the same league as mutual fund behemoths like BlackRock and Fidelity and banking giants like JPMorgan Chase.

On Thursday, Blackstone became the first in the private equity industry to hit that level, boasting in its latest quarterly earnings report that it managed just over $1 trillion in assets as of the end of June.

For firms like Blackstone, attaining that size cements their position as a major player in mainstream finance. On Main Street, the firm is perhaps best known for striking debt-fueled takeovers of companies, even if in reality it has long since branched out into an array of other businesses, from lending to real estate.

“This milestone reflects the extraordinary trust we have developed with our investors,” Stephen A. Schwarzman, Blackstone’s co-founder and chief executive, said in a statement. He added that he saw “a vast opportunity for further expansion.”

Blackstone, which began as a two-person shop in 1985 overseeing $400,000, has become a dominant force in the so-called alternative investments industry. It rose to prominence with leveraged buyouts, the kinds of transactions made famous by “Barbarians at the Gate” and other chronicles of 1980s finance.

These firms have since branched out into nearly every corner of finance. In 1991, Blackstone began its real estate business, which is now its largest division and the nation’s biggest landlord. It has also moved into hedge funds, credit trading, infrastructure investing and more.

That sort of growth helped transform Blackstone from depending on striking deals for the majority of its fees to becoming an asset gatherer that can charge management fees on funds it oversees. Blackstone executives have also benefited greatly: Mr. Schwarzman took home $1.26 billion in pay and dividends last year.

Expansion has also exposed Blackstone to more challenges. The swelling size of investment firms like Blackstone has raised questions in Washington about their omnipresence throughout the American economy, from housing to corporate lending to insurance and beyond.

Mr. Schwarzman himself has sometimes drawn scrutiny for his significant donations to Republican politicians, as well as his interactions with former President Donald J. Trump, a longtime acquaintance, during his administration. (Mr. Schwarzman has said he would not back Mr. Trump in the 2024 presidential campaign.) Jonathan D. Gray, Blackstone’s president and the firm’s heir apparent, is a major donor to Democratic candidates.

Several of Blackstone’s businesses have been buffeted by economic headwinds recently, reflected in a nearly 40 percent fall last quarter in the firm’s distributable earnings, a measure of the money that could be paid out to investors. The firm’s private equity division has been hurt by a lack of cheap financing, as the Federal Reserve has raised interest rates. Concerns about debt costs and plunging office occupancy rates also spurred investors to pull their money from Blackstone’s flagship real estate fund, leading the firm to limit withdrawals.