Kiesha Thompson was allegedly deliberately struck by a four-wheel drive while walking home on a footpath after dropping her daughter at daycare in Daisy Hill, south of the city, on Friday.
The 23-year-old died in hospital that night.
Police charged Tyler Scott William James with murder as a domestic violence offence on Monday after he was arrested at Logan Central.
Detective Inspector Chris Knight said on Tuesday that James and the victim were in an intimate relationship in the months before the alleged murder.
Police will allege their relationship formed part of the motive for the attack.
James' case was mentioned in Brisbane Magistrates Court on Tuesday.
Police earlier charged James' girlfriend, 24-year-old Larissa Rita Mae-Leigh Sant, with murder.
Det Insp Knight said James was allegedly involved in the planning of the murder but Sant was the sole driver of the car.
"We will be alleging that (James) was a participant in the planning and preparation of the offence," he told reporters on Tuesday.
He said James and Sant were "equally involved" in the offence.
Det Insp Knight called it a "horrendous crime" that would have a "tremendous" impact on Ms Thompson's family.
"I've been investigating for more than 30 years and spent a large portion of my career doing homicide and death investigations but there are features we have identified in this investigation that will stay with me," he said.
Ms Thompson's family called the "horrific and senseless" tragedy a "cowardly act" in a video released by police on Monday.
Her sister, Keyara, said the pain of losing her sibling could not be put into words.
"We are struggling with the enormity of her absence in our life," she said.
Her family vowed to take care of her baby daughter who was "the absolute light of her life".
"We are here to support her (daughter) throughout her whole life," her brother Koby Torto said.
James, 27 of Acacia Ridge, did not appear in person in court while his charge was briefly mentioned on Tuesday.
James' solicitor, Catherine Stewart, requested that the matter next be heard as a committal mention before Beenleigh Magistrates Court on July 31 with his co-accused Sant.
Magistrate Julian Noud on Tuesday ordered James be remanded in custody with his charge to be mentioned with Sant's at the same hearing but excused him from appearing in person.
Sant was remanded in custody after her matter was mentioned in Ipswich Magistrates Court on Monday.
