Once a relative unknown, Iraqi PM Abadi seeks second term

* A compromise candidate in 2014, Abadi has surprised

* Former engineer declared victory over Islamic State

* Abadi seen as more inclusive than main Shi'ite rivals

By Raya Jalabi and Ahmed Aboulenein

BAGHDAD, May 7 (Reuters) - Few outside Iraq knew the name Haider al-Abadi in 2014 when he was plucked from relative obscurity to lead a nation in chaos.

A compromise candidate floated after his predecessor Nuri al-Maliki was sidelined in a power struggle, Abadi became prime minister in September that year, two months after Islamic State ran rampant across Iraq and declared its so-called caliphate.

Four years on, Abadi has defied the expectations of an army of sceptics.

He has declared victory over Islamic State, diffused sectarian tensions fanned by Maliki, thawed frosty relations with Sunni Arab neighbours, and maintained Iraq's fragile unity in the face of an ill-fated Kurdish bid for independence.

Abadi has also balanced the competing and colliding interests of his two main backers, Iran and the United States.

A former electrical engineer once in charge of servicing BBC elevators during years of voluntary exile in the United Kingdom, Abadi is banking on his achievements in office to win a second term at May 12 elections.

But victory is far from certain.

Like all Iraqi prime ministers since Saddam Hussein's fall in 2003, Abadi, 66, belongs to the country's Shi'ite Arab majority. But this year the Shi'ite vote, typically enough to produce a clear victor who can claim the right to form a governing coalition, is split.

Besides Maliki, who appeals to Shi'ites wary of power-sharing with minority Sunnis and Kurds, Abadi is also up against Hadi al-Amiri, a military commander seen as a war hero for helping defeat Islamic State.

Knowing he cannot rely on Shi'ite votes alone, Abadi is looking to draw upon a wider voter base. He has been campaigning throughout Iraq with his cross-sectarian "Victory Alliance" list, the only one to run in each of Iraq's 18 provinces.

Badr al-Fahl, a Sunni lawmaker from Salahuddin province seeking his fourth term in parliament, said he chose to run on Abadi's list because it was cross-sectarian and inclusive.

"This is the first list since 2003 to run in all 18 provinces with Sunni, Shi'ite, Kurdish, Christian and Yazidi candidates," he told Reuters at the Victory Alliance headquarters in Tikrit. "Abadi does not use sectarian rhetoric and wants to build the country. The next phase is all about reconstruction and building."

Fahl said Abadi had given political allies in Sunni provinces complete freedom over selecting the candidates on his list. In Salahuddin, for example, the Victory list is all Sunni.