The 27-year-old victim, a mother of three children, was hospitalized after Tuesday's attack, in southern Austria, which left her with serious burns.
She has already undergone two operations having suffered second and third degree burns to 40 percent of her body.
The explosives package was detonated when she picked it up outside her apartment in the town of Guttaring, in Carinthia state.
Local police announced Thursday that they had arrested her former husband, and an accomplice, who admitted carrying out the attempted murder.
The 29-year-old accomplice, a member of the military, placed the package outside the woman's home, rang the doorbell then ran off.
The former husband, himself ex-military, was hiding nearby and remotely detonated the explosives, the police said in a statement.
He was arrested on the day of the attack while his accomplice was arrested on Thursday.
Police said the pair had tested homemade explosives over the summer, carrying out explosions in a forest after acquiring the components via the internet.
Of the 73 homicide victims in Austria last year, 41 were women, according to interior ministry figures.
Half of the killings in 2018 were carried out by a member of the victim's family.