A citizen of India, who is absent from the country owing to employment, education etc, and has not acquired citizenship of any other country are known as Overseas Voters and are eligible to be registered as a voter in the address mentioned in their Indian passport.
Please check website: http://ecisveep.nic.in/voters/overseas-voters for more information.
Election Commission of India (ECI) has recently launched the online service for citizens of India, including Non-Resident Indians called the National Voters’ Service Portal (NVSP) which provides online registration facility besides all other services related to electoral registration i.e. correcting entries or change in address, searching name on electoral roll.
Please visit: www.nvsp.in and enrol yourselves.