Sia is pulling the plug on her marriage ... because she just filed for divorce.

The "Unstoppable" singer beelined it to court Wednesday and filed to divorce her husband, Daniel Bernard, after only 26 months of marriage.

According to the docs, obtained by TMZ, Sia lists Tuesday as the date of separation ... meaning she wasted almost no time filing to end things.

Sia is also going with the boilerplate "irreconcilable differences" as the reason for the split.

There is a minor child involved ... Sia and Dan have an 11-month-old baby, Somersault Wonder Bernard, and Sia is asking for legal and physical custody of the kid but is open to visitation rights for Dan.

As for spousal support ... Sia checked the box to terminate the court's ability to award spousal support to her estranged husband. It's unclear if there is a prenup.

Sia and Dan got hitched in December 2022 and this is her second divorce. She previously divorced her first husband, Erik Lang, in 2016 after a little over 2 years of marriage.