* Opposition candidate won surprise poll victory
* Gambia's authoritarian Jammeh has ruled for 22 years
* Economy in ruins, country an international pariah
By Edward McAllister and Joe Bavier
DAKAR, Dec 2 (Reuters) - A decade and a half ago, Adama Barrow was working 15-hour shifts as a security guard at retailer Argos in north London, harbouring dreams of making his mark as a real estate developer.
On Friday, he was declared president-elect of his homeland, the tiny riverside West African nation of Gambia, ending over two decades of rule by Yahya Jammeh, a feared authoritarian who once said he would rule for "a billion years".
Gambians are now looking to the man nicknamed "no drama Adama" because of his cool, calm collectedness, to reverse 22 years under Jammeh's erratic rule that have hurt the economy and made the popular holiday destination a regional pariah.
It is not a job that the soft-spoken Barrow - a member of the Fula ethnic group from rural eastern Gambia - had sought out. He only learnt he was even being considered as a party leader when he turned up for the vote in September.
Jammeh, a former army officer, seized power in a 1994 coup before he had even turned 30. In contrast, Barrow, 51, was unknown to most of his compatriots before the main opposition United Democratic Party's (UDP) leadership election.
"(Before) Barrow came to vote for a new UDP party leader, he didn't even know his name was on the ballot," said Ramzia Diab, a leading member of the coalition that backed his run for the nation's presidency.
In April, small protests in Banjul calling for electoral reform had led to dozens of arrests. Two UDP members died in custody while others were sentenced to jail time.
When the UDP's then-president Ousainou Darboe, who had lost to Jammeh in four successive elections of questionable credibility, was handed a three-year prison sentence, the party needed a leader.
"(Barrow) was absolutely thrust into this position," said Jeffrey Smith, founding director of the advocacy group Vanguard Africa. "He took hold of that leadership and played a seminal role in rallying the disparate opposition leaders around him."
"THE OPPOSITE OF JAMMEH"
Until he took control, Barrow was mainly known within the UDP, which he joined in 1996, for his methodical management of the books as party treasurer.
But he quickly proved to be an adept opponent, turning Jammeh's attempts to stamp out dissent against the administration and galvanising a coalition of eight parties to back a single candidate in the Dec. 1 vote. They chose him.
"I am overwhelmed by your confidence," Barrow said timidly in a speech accepting the candidacy.
Barrow plans to reverse some of Jammeh's capricious acts, including stopping Gambia's withdrawal from the International Criminal Court announced last month, his spokesman Karamaba Touray said. He will also ask to rejoin the Commonwealth and nullify Jammeh's declaration of Gambia as an Islamic republic.
"He is the absolute opposite of Jammeh. He wants to restore democracy, it will be entirely different," Touray said.
The biggest test of this ambition comes in three years' time: Barrow has pledged to step down by then to open up newly democratic Gambia's political space. (Editing by Tim Cocks and Alison Williams)
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