SEOUL—Imprisoned for the past seven months, Samsung’s de facto leader Lee Jae-yong walked free, after South Korea’s justice ministry pointed to the national economy in granting him parole earlier this week.

He was released roughly a year early from a 30-month sentence for bribing South Korea’s former president. As he left a detention center near Seoul on Friday, Mr. Lee, wearing a gray suit and a face mask, apologized to the nation. “I am well aware of all the worry, criticism, concern and expectations I face,” said the 53-year-old grandson of Samsung’s founder.

Now, he has to prove his reprieve was justified.

When Mr. Lee was in prison, his supporters argue, Samsung delayed big investments, avoided major acquisitions and lacked strategic direction. So goes life for the head of a dynastic South Korean conglomerate where power largely centers around a single ruling family member.

His to-do list is significant. Samsung needs to still make final calls on where to build U.S. factories for chips and electric-vehicle batteries. Its biopharmaceuticals production unit needs to land more contracts to become a bigger player in global Covid-19 vaccine production. Extra spending is necessary to gain ground in the chip-foundry sector, semiconductor-industry experts say.

The Samsung chief, known in the West as Jay Y. Lee, won’t be able to formally return to work immediately. Under South Korean law, individuals who commit economic crimes are subject to a five-year employment ban, while those paroled face restrictions on overseas travel.

But the Samsung head is likely to get an employment exemption in the coming months, if not weeks, legal experts say. Economic factors were cited as justifications for his parole—a sign that the government wants Mr. Lee back at work, they said. The Justice Ministry declined to comment on the matter.

From the Archives

Lee Jae-yong, Samsung’s de facto chief, spent years burnishing his image as a modernizer at one of South Korea’s most hierarchical firms. He now finds himself at the center of a decidedly old-school Korean imbroglio. Photo: SeongJoon Cho/Bloomberg News The Wall Street Journal Interactive Edition

Samsung has dozens of affiliates in sectors including consumer electronics, chips, construction and life insurance. Each has professional managers and independent boards that handle day-to-day operations. But Mr. Lee must give the final nod for major moves.

Once back at work, Mr. Lee will need to demonstrate that his return shakes Samsung out of its strategic paralysis, given that his parole—and likely work-ban exemption—have been contentious with the South Korean public. The move could come in the form of an investment plan or a merger, said Park Sang-in, a corporate-governance expert and professor of public administration at Seoul National University.

“Lee Jae-yong and Samsung will be under pressure to show something. That Lee’s coming back made a difference,” said Prof. Park, who has long studied South Korea’s family-led conglomerates.

One of the major decisions that Mr. Lee will have to make when he rejoins Samsung is the location of a planned U.S. semiconductor plant. Samsung plans to invest approximately $17 billion in the contract chip-making facility that would be a key pillar in the Korean company’s bid to compete against Taiwan Semiconductor Manufacturing Co. and Intel Corp. , which recently announced plans to become a major foundry player.

Samsung, which was considering sites in Arizona, Texas and New York for the new plant since at least January, hasn’t reached a decision after more than six months.

Compared with TSMC and Intel, Samsung has been comparatively slow in its investment decisions, which could hurt the South Korean company in the coming years, said Ahn Ki-hyun, vice president of the Korea Semiconductor Industry Association.

Samsung has earmarked nearly $150 billion for expanding its foundry and chip-design business through the end of 2030. But TSMC will plow $100 billion into extra chip capacity in just the next three years. Intel’s planned spending is lower, though it is exploring a deal to buy GlobalFoundries Inc. for around $30 billion, The Wall Street Journal reported in July.

“The investments Samsung has made now will allow it to only maintain its current market share. For meaningful expansion, M&As may be necessary,” said Kim Yang-paeng, a senior researcher at the Korea Institute for Industrial Economics and Trade, a state-run think tank.

Samsung Electronics, which has more than $80 billion in net cash and is based in Suwon, South Korea, hasn’t sprung for a major acquisition in roughly four years. But on its second-quarter earnings call last month, the company said it would seek a significant acquisition within three years, citing potential target areas in artificial intelligence, 5G mobile networks and automotive tech.

A Samsung SDI battery for electric cars.

Photo: Yonhap News/Zuma Press

Samsung SDI Co. , in its earnings call last month, said it planned to enter the U.S. electric-vehicle battery market, but didn’t provide a time frame. The company is scouting multiple U.S. sites for a battery plant, including Illinois, a Samsung SDI spokesman said.

Samsung’s pharmaceutical business could also attract Mr. Lee’s attention. The company’s contract drug-manufacturing arm signed a deal in May to provide fill-and-finish packaging for hundreds of millions of Moderna Inc.’s Covid-19 vaccine. It is working to add other forms of capacity for messenger RNA vaccines, but would need to expand the arrangement with Moderna or strike new ones with other pharmaceutical companies, industry analysts say.

“Lee Jae-yong will have to really show his management capability by turning Samsung’s situation around,” said Mike Cho, a corporate-governance expert who teaches business at Korea University in Seoul.

Write to Jiyoung Sohn at jiyoung.sohn@wsj.com