The energy-rich nation of 17 million people began accession talks in 1996 but the negotiations were complicated by its membership of the Russian-led Eurasian Economic Union which also includes Armenia and Belarus.
President Nursultan Nazarbayev hailed the completion of talks, saying his government would continue supporting agriculture even after the country formally becomes the WTO's 162nd member in December.
"This is a historic event for us," the 74-year-old said in a video address to the nation.
"Membership of the WTO will provide our enterprises with access to foreign markets, and consumers with a wide selection of goods and services," said Nazarbayev, adding that 90 percent of Kazakhstan's trade was with WTO members.
Kazakhstan's key trade partners Russia and China have been members of the WTO since 2012 and 2001 respectively.
Talks on Kazakhstan's entry concluded at a Working Party meeting on June 10 in Geneva, with members of the Working Party celebrating the end of "one of the most challenging negotiations" in the international organization's history.
Speaking Monday after the country's accession package won members' formal approval, European Union Ambassador to the WTO Angelos Pangratis congratulated the Kazakh negotiating team for behaving "diligently and proactively" during the process.
The country is expected to be represented at a WTO ministerial conference in Geneva in December.
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