Lordstown Motors Corp. on Thursday said Daniel Ninivaggi, a longtime automotive industry executive and lieutenant to billionaire Carl Icahn, has joined the electric-truck startup as chief executive and a member of the board.

Mr. Ninivaggi once served as CEO of Icahn Enterprises LP and ran Icahn’s automotive aftermarket service network and parts distribution businesses. He also served as co-chairman and co-CEO of Icahn’s Federal Mogul unit before its sale to Tenneco Inc.

As of June 30, Carl Icahn, the billionaire activist investor, didn’t hold a stake in Lordstown Motors.

Lordstown Motors plans to begin production of electric pickup trucks at a former General Motors Co. assembly plant in Ohio next month, but the company’s stock has been slammed in recent months due to several challenges that have emerged since it went public last fall.

Shares were up nearly 25% in Thursday morning trading.

Mr. Ninivaggi, 57, takes over a startup that is still trying to get its first model, the Endurance pickup, to market, an endeavor made more difficult by the company’s shaky financial position and poor stock performance.

Lordstown Motors disclosed last spring it lacked funds to start commercial production and that there were doubts as to whether it would be able to continue as a going concern.

Company executives have said they are trying to raise new capital and pivot to a new strategy, in which the company aims to generate revenue by offering unused parts of its factory to other businesses for manufacturing.

The new CEO takes over from founder and former Chief Executive Steve Burns, who resigned in June along with other top executives. The departures followed a report from a company board committee that found inaccuracies in some of the company’s disclosures around its preorder book for the forthcoming truck.

Lordstown Motors has also disclosed that the Securities and Exchange Commission and the Justice Department are investigating aspects of its business, including its statements regarding preorders and its merger with a special-purpose acquisition company, or SPAC, that took it public.

Mr. Ninivaggi serves as chairman of Garrett Motion Inc. Lordstown Motors said Mr. Ninivaggi will receive an annual salary of $750,000 and an annual bonus with a target of 125% of his base pay.

Angela Strand, who has been serving as executive chairwoman, will continue as nonexecutive chairwoman, the company said.

Lordstown Motors executives have said the company is still on track to start limited production of the Endurance in late September.

Lucid, Fisker, Rivian and Canoo are among the well-funded startups racing to release new electric vehicles. WSJ asked CEOs and industry insiders how new auto companies plan to challenge Tesla’s market dominance and take on legacy car makers. Photo composite: George Downs The Wall Street Journal Interactive Edition

The company aims to sell its electric-pickup truck to commercial fleet operators who intend to use the vehicle for business purposes. It has said that electric models have an advantage as work vehicles because they can reduce fuel and maintenance costs for owners.

Company executives have stressed the importance of being first to market with a full-size electric pickup, aiming to beat Ford Motor Co. and other traditional auto makers.

Earlier this year, Ford unveiled an all-electric version of its bestselling F-150 pickup truck. That model is slated to hit dealer lots in 2022 with a price that starts at about $10,000 lower than the suggested $52,500 price of the Endurance.

After the departure of Mr. Burns in June, Lordstown Motors hired turnaround specialist AP Services, LLC, a subsidiary of AlixPartners LLP.

Since then, the company has showcased to investors the massive factory it took over from GM. Earlier this month, executives said they were exploring deals to bring in more cash, including through contract manufacturing for other companies or offering them unused factory space.

Write to Ben Foldy at Ben.Foldy@wsj.com