The 2015 dam collapse killed 19 people and unleashed a deluge of thick toxic mud into villages, fields, rainforest, rivers and the ocean.
The Fundao tailings dam at an iron ore mine in the mountains of Minas Gerais state was managed by Samarco, co-owned by BHP and Brazilian miner Vale.
"I will produce a judgment as soon as I can," said judge Finola O'Farrell as she announced the end of the trial.
The London High Court hearing, which began in October, heard evidence on behalf of BHP and hundreds of thousands of claimants in relation to the dam collapse that may trigger a payout worth billions of pounds (dollars).
At the time of the disaster, BHP had global headquarters in Britain and Australia.
Should the court find BHP liable, a further trial would be held to determine the amount of compensation.
- Awaiting verdict -
"I'm hoping (for a judgment) towards the end of the second quarter, perhaps in June or July this year," said Tom Goodhead, of law firm Pogust Goodhead, which brought the case.
"And then there's another trial... which has been scheduled for October 2026 in the event that it's necessary to prove the damages that people have suffered," he told AFP.
Goodhead added that for the victims, "accountability" was even more important than money.
A separate case in Brazil has seen Vale and BHP offer to pay around $30 billion in compensation.
This was increased from almost $25 billion at around the start of the London trial.
"We respect the London process," said Fernanda Lavarello, head of corporate affairs at BHP Brazil.
"We continue to defend ourselves here (in London), but we think that Brazil is the right place for us to address all these outstanding issues," she told AFP.
More than 620,000 complainants -- including 46 Brazilian local authorities, companies and Indigenous peoples -- are seeking an estimated GBP 36 billion ($47 billion) in damages in the civil trial.
BHP, while acknowledging that a "tragedy" occurred, argues that it cannot be deemed to be the "direct polluter", as the dam was managed by Samarco.
- 'Hopeful of justice' -
The dam collapse in the town of Mariana unleashed almost 45 million cubic metres (1,590 million cubic feet) of highly toxic mining waste sludge, flooding 39 towns and leaving more than 600 people homeless.
"I'm here for justice," Pamela Fernandes, who lost her five-year old daughter Manu in the tragedy, told AFP outside court.
"I will feel relief when I hear that the company will pay for what it did."
According to the victims' lawyers, BHP was aware that the accumulation of toxic sludge, estimated at 1.3 million tonnes per year, far exceeded the annual limit set -- a build-up which they say contributed to the disaster.
BHP and Vale estimate that more than 430,000 complainants have already received compensation, including more than 200,000 party to the London case.
Attending the hearing's final day was Mariana's mayor, Juliano Duarte.
"Today we came to follow the final part of the trial... seeking justice for the city of Mariana, since it was the city most affected by the dam collapse," he said.
"We hope to have better justice in London, to receive amounts commensurate with the scale of the tragedy."
BHP has noted that the Renova Foundation -- which manages compensation and rehabilitation programmes, funded by BHP, Vale and Samarco -- has paid out more than $7.9 billion in emergency aid.
The Australian mining giant has also said the quality of water in the river system contaminated by the fallout has returned to pre-disaster levels.
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