Timor Leste, Southeast Asia's poorest nation with 1.4 million people and slightly bigger than Qatar, applied to join the 10-member Association of Southeast Asian Nations in 2011 and was granted observer status in 2022.

The nation gained independence in 2002 from neighbouring Indonesia, following a 1999 referendum overseen by the United Nations, and shares a border with the Indonesian province of East Nusa Tenggara.

Two of its independence heroes now lead the country: President Jose Ramos-Horta, who won the Nobel Peace Prize in 1996 for his efforts, and Prime Minister Xanana Gusmao.

Decades after Ramos-Horta raised the idea of joining ASEN in the 1970s when Timor Leste was still a colony of Portugal, the country will be formalised as a member at the October 26-28 ASEAN leaders summit, which Malaysia chairs.

Timor-Leste is trying to diversify its nearly $2 billion economy away from its heavy reliance on dwindling oil and gas reserves.

Analysts say the accession to ASEAN will benefit its newest member but they worry about how it will fare as the group's smallest economy. ASEAN's collective gross domestic product is $3.8 trillion, with Indonesia alone making up $1.4 trillion of that.

Ahead of the summit, Malaysian Prime Minister Anwar Ibrahim recalled other members were also poor when the bloc was first formed.

"I'm very optimistic that ASEAN as a community can continue to engage more and assist, as we have benefited from the assistance of many countries (including) the West and China," he told reporters on Wednesday.

ASEAN Secretary General Kao Kim Hourn has said joining ASEAN will amplify East Timor's "voice in international forums while securing its strategic interests through an established network of diplomatic and economic support." 

Ramos-Horta has called the membership a long-held dream.

"The road to ASEAN is more difficult than the road to heaven," he said in a speech at the group's headquarters in August.

Parker Novak, a Timor Leste expert at the International Republican Institute, said the country's leadership sees ASEAN "as giving them additional political legitimacy in the region."

Marty Natalegawa, a former foreign minister who oversaw Timor Leste's ASEAN application, said the bloc would shield Timor Leste against the geopolitical push-and-pull among major powers such as the United States and China.

"It provides assurances that Timor-Leste's position and future development and outlook will be akin to ASEAN's own," Marty said.

However, Guteriano Neves, an economic development researcher in Timor Leste's capital Dili, worries the country's low productivity and lower-quality governance will limit the economic benefits of membership.

Neves said membership may pressure Timor Leste's government to enact institutional reforms to attract foreign investment. 

"Economically speaking, that is the hard question that I think we haven't really found the answer to," Neves said. "It's very hard for Timor-Leste to compete in the ASEAN market."