The change was passed in March by the Legislative Assembly, controlled by Bukele's party, and would apply to people convicted of committing or acting as an accomplice to crimes including homicide, femicide, rape and gang membership. The measure was pushed forward by Bukele's cabinet.
Previously, the maximum sentence in El Salvador was 60 years for adults and less for youths. The reforms slated to take effect April 26 would create new criminal courts to try cases.
They also stipulate a mandatory review of life terms decades into the sentences, depending on the age of the convict and the gravity of their crimes.
Critics say the reforms are just the latest harsh move by Bukele more than four years into his war on gangs.
Following a burst of gang violence in 2022, Bukele announced a then-temporary state of emergency, which has become the new normal in the Central American nation as it's been extended for years.
He suspended constitutional rights and locked up more than 1 per cent of El Salvador's population, often on vague charges with little evidence. Prisoners are often judged in mass trials and lawyers regularly lose track of where their clients are.
In one mass trial in 2025, alleged gang members were handed sentences of hundreds of years.
Officials in Bukele's government have previously vowed that gang members detained "will never return" to the streets.
Under the crackdown, Bukele's government has detained around 91,650 people in El Salvador. Bukele has said that less than 10 per cent of those people have been released.
It has fuelled accusations of human rights abuses and arbitrary detention, but also sharply dipped homicide rates in a country long terrorised by gangs, handing Bukele soaring popularity levels.
The right-wing ally of US President Donald Trump has been fiercely criticised for weakening checks and balances and undermining El Salvador's fragile democracy.
The sentencing changes are the latest in a slew of constitutional reforms jammed through by Bukele and his allies.
Last year, the government pushed through one of its most contentious reforms that would eliminate presidential term limits, paving the way for Bukele to remain in power indefinitely.
Emboldened by Bukele's alliance with Trump, the government has also gone after its enemies, detaining critics and activists, and increasingly forcing journalists and opposition voices to choose between exile or prison.
