The window of the Rochdale Boulevard building was vandalized with blue spray paint saying "crook."
The incident happened early Sunday at around 1:30 a.m., according to security camera footage released on the Saskatchewan Party's Twitter account.
Premier Brad Wall tweeted about the graffiti on Sunday afternoon.
"Last night some jackwagon vandalized @SaskParty HQ w/ graffiti," he wrote.
Wall asked anyone who recognized the "said jackwagon" to call Regina police at 306-777-6500 or call Crime Stoppers at 1-800-222-8477 or report online.