Russian carrier S7 Airlines is to join the Oneworld alliance, and will begin integrating itself with the airline group from June.
S7's accession has been "unanimously" accepted by the 10 current members of Oneworld.
The Moscow-based carrier, sponsored by British Airways, is to begin an 18-month alignment process ahead of becoming a full member in 2010.
Through S7, Oneworld will have access to another 54 destinations of which 35 are in Russia.
It will also provide the alliance with connections to eight countries: Armenia, Azerbaijan, Kazakhstan, Kyrgyzstan, Moldova, Tajikistan, Turkmenistan and Uzbekistan.
S7 will take initial steps towards Oneworld on 1 June when its network will be added to the alliance's round-the-world fare packages.
But the integration process, says the alliance, will also involve switching information technology systems and changing internal processes and S7's formal accession date will be determined "once all its pre-joining requirements are sufficiently progressed".
S7 chief Vladimir Obyedkov says Oneworld membership will be one of the "most significant" steps in the airline's history.
Oneworld says the acceptance of S7 will expand its global network to nearly 750 destination in total, and give the alliance a combined fleet of 2,300 aircraft transporting over 330 million passengers.
Russia has long been viewed as a region of relatively low alliance coverage. Following the decision of Aeroflot to join SkyTeam, both Star Alliance and Oneworld have been left with difficult choices as a result of turmoil in the Russian airline sector.
Oneworld managing partner John McCulloch says that S7 will fill one of the alliance's "few remaining membership 'white spaces'" and says the Russian carrier "matches our alliance's demanding quality requirements".