Damien Mantach, the former Liberal Party state director for Victoria, has been sentenced to five years in prison after pleading guilty to defrauding the party of $1.55 million, partially in an attempt to save his disintegrating marriage.

He will be eligible for parole after two years and eight months.

When the sentence was read out by Judge Liz Gaynor of the Victorian County Court on Tuesday morning, a man in the courtroom was heard to say "Oh, bloody hell."

Judge Gaynor told Mantach, who was dressed in a dark suit and blue tie, that "the only option open to this court is a term of imprisonment".