Argentina has lowered its voting age to 16 from 18, a change that could help politically ailing President Cristina Fernandez court the youth vote ahead of 2013 mid-term elections.
Dozens of opposition members of the lower house of Congress walked out of the rancorous late-night session on Wednesday just before the measure won final approval by a vote of 131 to 2.
Fernandez, who polls well among younger voters, has not ruled out a bid by her supporters to change the constitution to allow her to run for a third term in 2015.
Legions of youthful activists have joined the "Campora" movement, known for its rowdy demonstrations in favour of Fernandez's heterodox policies.
Drumming up support
Skeptics say the new law is aimed at drumming up support for the president before legislative elections scheduled a year from now.
Supporters say the measure aims to bring Argentina in line with progressive countries such as Ecuador and Brazil that have already extended voting right to people as young as 16.
Fernandez-allied lower house member Diana Conti said the bill "is neither opportunistic nor demagogic," but rather seeks "to widen the electoral base of our democracy."
The makeup of Congress after the midterms will be key to any effort by her allies to open the door to another candidacy.
The 59-year-old Peronist leader won a blowout re-election last year and no strong opposition figure has emerged since.
But her popularity has fallen to below 25 percent as the economy gets hit by sluggish world growth, slowing demand from top trade partner Brazil, high inflation at home and government-imposed currency and trade controls that hurt confidence.
More than a million new voters are estimated to be eligible to cast ballots now that the bill has passed both houses. The Senate approved the measure earlier this month.
You still have to be 18 in Argentina to get married or buy alcohol or cigarettes.
Voting is compulsory for Argentines between the ages of 18 and 70 but it will be discretionary for 16- and 17-year olds under the new law.