As the son and nephew of two Malaysian prime ministers, Mr Najib has an impeccable political pedigree but is burdened by the whiff of scandal and is not trusted by ethnic minorities in the multicultural country.
Prime Minister Abdullah Ahmad Badawi last week succumbed to intense pressure and agreed to quit after five lacklustre years in the job, paying the price for disastrous results in general elections.
Mr Najib is expected to win a vote to lead the United Malays National Organisation (Umno) in March and, by tradition, automatically become prime minister of the country.
But he will inherit a deeply divided party, with trust in the government at its lowest ebb and a resurgent opposition - headed by Datuk Seri Anwar Ibrahim - threatening to seize power.
He must also contend with a scramble for the party's newly vacated number-two spot, and a challenge from Umno veteran Tengku Razaleigh Hamzah who has said he will contest for the presidency.
'Najib will not have a free ride to the premiership,' political scientist Shaharuddin Badaruddin told AFP.
'Najib will have to deal with the issues in his past which will be resurrected and don't forget that many of Abdullah's supporters will now most likely throw their support for Razaleigh,' he said.
The 55-year-old politician is the longest serving cabinet minister, entering politics at 23 after the 1976 death in office of his father Abdul Razak, the country's second prime minister.
Mild-mannered and always dressed in immaculate suits, Mr Najib took a degree in economics at the University of Nottingham before returning to Malaysia in the mid-1970s to take on key posts at the central bank and the national oil firm.
A nephew of the country's third premier Hussein Onn, Mr Najib held several cabinet posts in the 1980 and 1990s, modernising the military as defence minister before becoming deputy premier in January 2004.
Although Mr Najib was a contender for the premiership, former prime minister Mahathir Mohamad chose Datuk Seri Abdullah to replace him in 2003.
But following a very public falling out with Mr Abdullah, Tun Dr Mahathir has backed Mr Najib for the top job in a campaign which intensified after dismal March polls that saw the government lose its two-thirds majority in parliament.
Under Malaysian tradition, Mr Najib has long been heir apparent to the premiership but a recent poll showed 44 per cent of voters believe he will not make a good leader.
'He is definitely equipped to become prime minister but he brings along with him a lot of baggage from the past that may haunt him,' Mr Shaharuddin said.
In the midst of a 1987 political crisis, Mr Najib as chief of the party's youth wing was linked to threats to bathe a keris, or Malay dagger, in the blood of Malaysia's minority Chinese.
The opposition has also accused Mr Najib of involvement in the alleged payment of large commissions to close associates for the purchases of two Scorpene submarines and 18 Sukhoi fighter jets - charges the government has denied.
Mr Najib has also fended off allegations from the nation's top blogger, Raja Petra Kamaruddin, who was thrown into detention under tough internal security laws after allegedly linking the deputy premier and his wife to a murder.
Mr Najib has repeatedly rejected any involvement in the 2006 slaying of 28-year-old Altantuya Shaariibuu, a Mongolian woman whose body was blown up with explosives in the jungle.
His close friend, Abdul Razak Baginda, is on trial for abetting the murder, and two police officers from a unit that guards the prime minister and his deputy have been charged with the killing.
'Najib should be able to survive the previous allegations and rumours but the bigger challenge will be to unite the party after months of infighting over the top post,' said Ms Tricia Yeoh, head of the Centre for Public Policy Studies.
'Najib will be an efficient, decisive performance-driven leader who improves the government delivery system and will be a big difference from his predecessor,' she said.
'But he'll also be stricter, harsher and we'll see a return of centralised decision making to Umno and the government coalition.' -- AFP
source: Najib faces tough ride
Straits Times, Singapore