The WTO General Council has approved oil-rich Kazakhstan's membership, finalizing almost 20 years of negotiations.
Kazakh President Nursultan Nazarbaev was present at the formal acceptance event at WTO headquarters in Geneva.
Kazakhstan has agreed to lower import tariffs and take further steps to attract more foreign investors.
However, Kazakhstan's domestic industrial and agricultural production levels remain relatively weak, as the country mainly relies on its oil revenue.
Experts say domestic firms may struggle if the market is flooded with foreign goods once the WTO terms are implemented.
Kazakhstan began WTO accession talks in 1996, but negotiations were repeatedly stalled, in part because of Kazakhstan's membership in the Russia-led Eurasia Economic Union.
Once the formal signing and ratification process is complete, Kazakhstan will become the WTO's 162nd member state.