Russia's lower house of parliament, the State Duma, has approved a treaty to annex the Crimean peninsula and the city of Sevastopol from Ukraine.
Approved by 443 lawmakers in an almost full chamber, the treaty is expected to be ratified today by the upper house Federation Council, despite being dubbed "illegal" by Ukraine, the US and other Western nations.
The State Duma passed a new constitutional law detailing the conditions and order of incorporating the two new subjects into the Russian Federation.
Russian Foreign Minister Sergey Lavrov said: "The decision to accept the Republic of Crimea into the Russian Federation is based on the free expression of the will of the multi-ethnic people of Crimea made in the referendum on 16 March this year.
"This decision corresponds to international law, including the principle of sovereign equality of the state and the people's right for self-determination, fixed in the UN charter as one of the main objectives of this organisation."
Approximately 96.8% of Crimean residents had voted in favour of joining Russia in the referendum, and the Black Sea peninsula declared independence from Ukraine the day after.
Meanwhile, the ratification has prompted the US to impose additional sanctions on more Russian diplomats, as well as other individuals and a bank accused of involvement in the annexation.
The draft introduces a transition period for the integration of Crimea and Sevastopol into Russia's economic, finance, credit, legal and state administration systems by 2015.