In new book, Dalai Lama tells followers to reject any successor chosen by China

The 89-year-old Buddhist monk’s declaration comes as Tibetan authorities—both sacred and secular—prepare to square off against China’s atheist Communist Party, which insists it alone has the right to select a new Dalai Lama after his death.

It is a high-stakes fight central to the survival of Tibetan religion, culture and politics.

Reincarnation is the traditional means of determining the succession of Tibet’s most important leaders. And the Dalai Lama’s rebirth will be a matter of religious and geopolitical importance, and one that China sees as strategically critical.

The current Dalai Lama has played a central role in galvanizing international support for the Tibetan cause and rallying the Tibetan people inside and outside of China. It could be years after his death before his successor, likely to be chosen as a young child, can assume the mantle of leadership.

In “Voice for the Voiceless: Over Seven Decades of Struggle With China for My Land and My People," a memoir published this week, the Dalai Lama decried “today’s dark period of Communist Chinese occupation" of Tibet, but said “nothing is immune to the law of impermanence."

He said that Tibetan people have made clear to him that the Dalai Lama’s lineage must continue, and he said the choice of a successor should be made according to traditional practices and that lamas and monks would conduct the search.

Born into a farming family in a village in northeastern Tibet, the current Dalai Lama was identified when he was 2 by senior Buddhist lamas.

The Dalai Lama’s book is being published Tuesday by HarperCollins, a unit of News Corp, the parent company of Dow Jones & Co., publisher of The Wall Street Journal.

The Dalai Lama began officially leading the Tibetans in 1950 at the age of 16, a month after the Communist government of China, established in 1949, began sending thousands of troops to the Himalayan region to assert control.

The Dalai Lama fled Lhasa, the historic seat of Tibetan Buddhism, in March 1959 after a Tibetan uprising broke out, sparked by fears that the Communist authorities were seeking to abduct him. He has lived in exile in India since.

After decades of serving as both the political and religious leader of Tibetans, the Dalai Lama separated the roles in 2011 and devolved political power to the head of the Tibetan government-in-exile, partly as an effort to ensure that the Tibetan movement would outlive him.

“Whoever chooses the 15th Dalai Lama is no longer choosing a political leader, they’re just choosing a religious leader," said Cameron David Warner, associate professor of anthropology at Denmark’s Aarhus University, whose research focuses on Himalayan Buddhism.

Even so, the presence of the Dalai Lama is critical to the legitimacy of the Central Tibetan Authority, as Tibet’s government-in-exile is known.

Tibetan experts point to a religious conclave scheduled to be held in early July, just ahead of the Dalai Lama’s 90th birthday on July 6, as a sign the Tibetan Buddhist leader could be preparing a fresh statement on his reincarnation.

“The continuity of the Dalai Lama institution is going to be crucial as that anchor that would unite all of us," said Thupten Jinpa, the Dalai Lama’s longtime translator, who assisted him on the book.

After Mao Zedong, whose rule brought violence and famine to Tibet, Deng Xiaoping made overtures through the Dalai Lama’s then Hong Kong-based brother, Gyalo Thondup, who died last month.

The then Panchen Lama, the most important figure for Tibetan Buddhists after the Dalai Lama, was released from prison, and then from house arrest, and China allowed exiled Tibetans to visit.

In the 1980s, the Dalai Lama dropped his pursuit of Tibetan independence, pushing instead for autonomy for Tibetans within China, partly because he doubted it was possible given Beijing’s hold on the region. But talks between his representatives and China failed to achieve results.

There have only been informal contacts between the Dalai Lama’s camp and Beijing since Chinese leader Xi Jinping came to power in 2012.

“I still remain convinced that given political will and vision on the part of the Chinese leadership, it would not be difficult for China to satisfy the needs of the Tibetans," he said.

The Dalai Lama’s account arrives at a precarious time for the Tibetan movement.

Tighter security and surveillance in Tibet in the wake of protests in 2008 and a wave of self-immolations, mainly by monks, have made it difficult for Tibetans to escape to India and has choked off the flow of information from the region.

Now, under Xi, China is intensifying a campaign to assimilate Tibetans, including sending young children to Chinese-language boarding schools and restricting their ability to study the Tibetan language.

The Trump administration’s suspension of much foreign aid will hit the Tibetan government in exile, cutting off about $14 million for various programs, according to Penpa Tsering, the leader of the exile administration.

On Feb. 28, at the start of the Tibetan new year, Secretary of State Marco Rubio said in a statement that “the United States remains committed to protecting the universal, fundamental, and inalienable human rights of Tibetans."

Despite the growing challenges for the Tibetan movement, the Dalai Lama called on Tibetans to remain hopeful—as he does.

Write to Tripti Lahiri at tripti.lahiri@wsj.com