Sia and her estranged husband Daniel Bernad are finally putting their nasty custody battle in the rearview mirror … reaching a settlement over their young son … TMZ has learned.

According to court docs, obtained by TMZ and submitted by Sia’s attorney, disso queen Laura Wasser, the former couple has agreed on a custody schedule for their son, Somersault Wonder Bernad, affectionately known as “Summi.”

Sia will remain his primary custodial parent, while Daniel will have generous visitation.

They’ve also worked out a schedule for holidays and vacations, agreed to work with a parenting plan coordinator, and established a process for deciding where Summi will attend preschool.

As TMZ reported … the “Unstoppable” singer and Daniel had been duking it out over custody of Summi … with Daniel previously accusing Sia of being a danger to their child and demanding full custody.

Sia denied the allegations and scored a victory when a judge rejected Daniel’s emergency custody request … though the two were later ordered into mediation to work out their differences.

This month marks one year since Daniel sought emergency custody and revealed an LAPD investigation into child pornography found on one of his computer hard drives. His request was denied … and Sia has remained Summi’s primary custodial parent ever since.

The former couple reached an agreement in April requiring Sia to pay Daniel $42,500 a month in child support, while sharing legal custody and splitting holidays with their son.

And there’s been plenty of money drama outside the custody fight … Daniel previously demanded more than $250K a month in spousal support … while Sia recently sold half her music catalog for a whopping $180 million.