Former President Donald Trump’s planned digital-media venture could quickly become a serious competitor in a crowded field of right-leaning sites and social networks, thanks to Mr. Trump’s prominence and online following.

Trump Media & Technology Group on Wednesday said it would create a social network called Truth Social, part of an effort by Mr. Trump to find a new social-media platform after he was banned by Facebook Inc. and Twitter Inc. in the wake of the Jan. 6 assault on the U.S. Capitol.

“Everyone...

Former President Donald Trump’s planned digital-media venture could quickly become a serious competitor in a crowded field of right-leaning sites and social networks, thanks to Mr. Trump’s prominence and online following.

Trump Media & Technology Group on Wednesday said it would create a social network called Truth Social, part of an effort by Mr. Trump to find a new social-media platform after he was banned by Facebook Inc. and Twitter Inc. in the wake of the Jan. 6 assault on the U.S. Capitol.

“Everyone asks me why doesn’t someone stand up to Big Tech? Well, we will be soon!” Mr. Trump, the chairman of Trump Media & Technology Group, said in a statement Wednesday.

The deal wouldn’t affect Mr. Trump’s ability to run for the White House again in 2024 if he chooses. There are no laws preventing Mr. Trump from continuing to run or own businesses while he is a presidential candidate or serves as president, if he were to win another term in the White House.

The new media company was born out of a meeting between Mr. Trump and Patrick Orlando, a former derivatives trader at Deutsche Bank AG, within weeks of leaving office this year, according to people familiar with the matter. Mr. Orlando is the chairman and chief executive of Digital World Acquisition Corp. , the special-purpose acquisition company that agreed to take Trump Media & Technology Group public.

The company didn’t disclose many details about the look and feel of Truth Social, which is expected to become available to select users next month and to be launched broadly early next year. Screenshots of the mobile app from a company presentation and Apple Inc.’s app store show a user interface very similar to that of Twitter and other social-media platforms.

A representative for Trump Media & Technology Group didn’t respond to requests for comment.

Beyond Truth Social, the company plans to launch a subscription streaming service that would feature entertainment programming, news and podcasts. The company didn’t disclose any launch time frame or potential subscription cost for the service. Scott St. John, an executive producer of TV shows including “Deal or No Deal’ and “America’s Got Talent” who the company said was tapped to lead the new service, didn’t respond to requests for comment.

Mr. Trump kept political allies—and some of his political staff—in the dark about the foundation of the company, people familiar with the matter said. In recent months, his eldest son, Donald Trump Jr.

, has taken an active role as a senior adviser to the new project and could have an executive role with the company, they said. The younger Mr. Trump has urged the company to use servers that would make it difficult for political enemies to target, the people said. Dan Scavino, a longtime aide and social media adviser for the former president, has had an informal advisory role on the construction of the social-media platform, they said.

Mr. Trump’s new venture will vie for attention with a bevy of websites and news channels that cater to conservative audiences, including Fox Corp.’s Fox News cable channel, Newsmax TV, the Daily Wire website and the Blaze, a media company started by the conservative media figure Glenn Beck. Fox Corp. and Wall Street Journal parent News Corp share common ownership.

It will also compete directly with other social-media platforms targeting conservatives, such as Parler and Gab as well as Gettr, which was launched by former Trump adviser Jason Miller earlier this year. In an interview, Mr. Miller said he had been in talks with Mr. Trump over the summer in an effort to get him to join the service, but they couldn’t come to the “right number.”

Parler didn’t respond to a request for comment on the launch of Truth Social. Gab, meanwhile, said it supported Mr. Trump’s new network and said users could still follow the former president on his reserved Gab account.

Mr. Trump had 89 million followers on Twitter, 33 million on Facebook and 24.5 million on Instagram, a unit of Facebook, before his accounts were suspended earlier this year, according to a Trump Media & Technology Group presentation.

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Existing conservative social-media platforms have much smaller user bases, according to app-analytics firm Sensor Tower. Three-year-old Parler has been installed by about 11.2 million smartphone users, compared with 1.1 billion for Twitter, which has been around for 15 years. Mr. Miller’s Gettr, which is just a few months old, has been installed by about 2.2 million smartphone users, Sensor Tower said.

Neil Patel, founder and publisher of conservative site the Daily Caller, said that Mr. Trump’s endorsement of the new venture would give it an initial advantage over some of its competitors in the conservative media sector.

“It could get to some serious scale,” Mr. Patel said. “Now, would others besides conservatives use it? I don’t know.”

Alan Knitowski, CEO of Phunware Inc., an enterprise software company that worked on apps for Trump’s 2020 presidential campaign, said Truth Social may find an audience with Americans who believe the leading social-media platforms have overreached in moderating content.

Some content will still be off-limits on Truth Social, including posts that the company believes “disparage, tarnish, or otherwise harm” Truth Social or Trump Media & Technology Group, according to the company’s terms of service.

“That strikes me quite clearly as an attempt to ensure that the site can’t be used by critics of Trump,” said Jillian York, director for international freedom of expression at the Electronic Frontier Foundation, a nonprofit civil-liberties group.

Chris Balfe, the former CEO of the Blaze, said in an interview that Mr. Trump’s streaming business could find success by signing up a large number of subscribers, adding that many subscription products aimed at conservative users have been successful.

“If this new service can sign up to 2 million subscribers, they could generate $240 million a year in revenue with minimal content expense,” Mr. Balfe said, assuming subscription fees of $10 a month.

Investors have responded enthusiastically to the launch of Mr. Trump’s media company. Shares of Digital World Acquisition, the SPAC taking Trump Media & Technology Group public, have risen nearly 10-fold since the announcement.

The SPAC has about $290 million that Mr. Trump’s media venture could use to fund its growth, though investors have the right to pull money out at $10 a share before the deal gets completed. They are much less likely to do that if the stock stays above that price since they would be losing money by withdrawing.

Mr. Trump’s new venture comes as his family business has faced financial troubles, including $400 million in debt due in the next few years. The pandemic has led to a drop-off in business at his hotels and golf resorts. Talks are continuing for the Trump Organizationto sell its rights to a hotel in Washington, D.C., that became popular among Republicans but has seen activity wane following Mr. Trump’s election loss. Lenders have indicated they are wary of doing business with Mr. Trump, and he is facing a number of investigations, including an indictment of the Trump Organization and its chief financial officer in New York.

—Benjamin Mullin and Alex Leary contributed to this article.

Write to Patience Haggin at patience.haggin@wsj.com and Michael C. Bender at Mike.Bender@wsj.com