A Quebec hit man who killed 27 people and tried to kill 12 others over three decades was apologetic as he pleaded guilty to his crimes, saying he won't likely be forgiven.

Gérald Gallant, seen in this sketch from a previous court appearance, pleaded guilty on Tuesday to 27 counts of first-degree murder and 12 counts of attempted murder. (CBC)

Gérald Gallant, an admitted contract killer during Quebec's bloody biker wars, pleaded guilty Tuesday in Quebec City to 27 murders and 12 attempted murders between 1978 and 2003.

As part of a plea deal, Gallant, 58, agreed to testify against 11 other people who allegedly ordered the killings or helped him carry them out.

Gallant is already serving a life sentence in the death of a bar owner and attempted murder of a bar patron in the Laurentian town of Ste-Adèle in 2001.

Under the plea deal, the length of his sentence remains unchanged. Gallant will also receive financial compensation — $50 a month to buy goods at the prison canteen.

Ten of the accused were arrested last week in a large-scale police operation that stretched from Montreal across central Quebec to the provincial capital. One person is still at large.

While gang members were the targets of the killings, there were also several innocent victims, the court heard.

Gallant apologizes to victims' families

On Tuesday, Gallant told the court he was sorry and added he knew that his crimes would be difficult, if not impossible, to forgive.

He said he decided to help the police as a way to repair the damage he caused.

Martine Bérubé, a spokesperson for Quebec's criminal prosecutions office, said emotions were running high in the courtroom.

"I can say the atmosphere was very emotional with the families of the victims being there, hearing the way he did the murders," said Bérubé outside the courtroom.

Among Canada's most prolific killers

Gallant's 28 total murder convictions and 13 attempted murder convictions make him one of Canada's most prolific killers.

However, his list is still shorter than Yves (Apache) Trudeau, one of the founding members of the Hells Angels in Quebec, who was sentenced to life in prison in 1986.

Trudeau pleaded guilty to 43 counts of manslaughter, part of a deal struck in exchange for information about fellow gang members.

With files from The Canadian Press