The court sentenced one of the women, a 20-year-old found to be the worst offender, to a term of 15 months in prison with a further 21 months suspended, the ATS news agency reported.
Her 22-year-old colleague received a one-year sentence and an additional suspended one-year term.
The January 20th 2013 fire, which caused an estimated 1.5 million francs’ ($1.65 million) damage, forced the closure of the municipal library to the public for almost three weeks.
Video surveillance cameras allowed investigators to track down the culprits who broke into the public facility for no apparent reason.
One of the women, originally from Kosovo, said she tried without success to open a safe in one of the offices then set fire to stationery on the spur of the moment, the prosecutor in charge of the case said earlier.
She was already known to police for multiple offences, including thefts and robberies, the prosecutor said.
According to the criminal court judges the pair’s culpablity was “serious”, ATS reported.
The penalty was “lenient” taking account of the regrets expressed by the convicted “which appeared to be sincere”.