Unofficial preliminary results Monday showed his Cambodian People's Party (CPP) won between 50 and 56 percent of the overall vote, which the CPP claims will land them 73 or 74 seats in the 123-seat National Assembly.
If correct, Hun Sen now stands to become the longest serving elected leader in the 10-member Association of South East Asian Nations (ASEAN) once Malaysia's prime minister Mahathir Mohamad retires next year.
As the son of a peasant Hun Sen never finished high school, but he nevertheless managed to emerge as a ruthless politician and has been a senior figure in Cambodian government for nearly 25 years.
Those years have included tragic wars, allegations of corruption on a massive scale, a coup and eventually five years of peace.
Hun Sen defected from the Khmer Rouge amid bloody purges to Vietnam, then returned with Hanoi's invading forces to oust the ultra-Maoists in 1979.
The one-eyed former guerrilla was then put in charge of foreign affairs for the Revolutionary Council and made foreign minister in May 1981 after winning a seat in Vietnamese-sponsored elections.
He became chairman of the Council of Ministers, effectively prime minister, in January 1985 and found that aid from the Soviet Union was drying-up as the Cold War was entering its final stages.
Turbulent path to power
Realising this would eventually lead to the end of Vietnamese occupation, Hun Sen began negotiating the return of Cambodia's revered monarch King Norodom Sihanouk.
Hanoi pulled its troops out of Cambodia in 1989 and elections were held under United Nations stewardship in 1993, two years after the Paris peace accords.
The royalist FUNCINPEC party scored an upset victory resulting in a power-sharing arrangement with Prince Norodom Ranariddh as first prime minister and Hun Sen as second prime minister.
An acrimonious co-habitation lasted until 1997 when Ranariddh was ousted in a bloody coup and Hun Sen assumed the top post as leader of the CPP.
Elections in 1998 cemented his position as prime minister and Hun Sen leapt into a program of constructing roads, bridges and schools.
But nagging question marks over his legitimacy as leader persisted.
FUNCINPEC and the opposition Sam Rainsy Party (SRP) vehemently protested the CPP victory with allegations of rigging and widespread intimidation. Further violence followed the poll, including bloody street-fighting in the capital.
Legitimacy at last
Some extreme-right Republicans in Washington later called for regime change in Cambodia and even tied extra funding to this donor-dependent economy with the removal of Hun Sen at these elections.
Even more moderate officials in Washington and the European Union have linked future financial aid to the success of these elections, which have been widely hailed as the best yet.
While previous elections were marred by violence and assassinations, this poll was noted for its quiet lead-up and peaceful polling day, with Hun Sen casting his vote as overwhelming favourite to win.
Perhaps the greatest sign of changing times in Cambodia occurred in Pailin, the remote northwestern former stronghold of the Khmer Rouge regime which once did battle with Hun Sen during a civil war that ended in 1998.
There, a former bodyguard of the late Khmer Rouge leader Pol Pot stood for his former enemy, the CPP, and won.