The fundraising, announced on Wednesday, will go towards the construction of one of Britain's biggest mines near Whitby, North Yorkshire.
Around 2,000 construction jobs will be created and a further 2,500 will be employed when the plant is fully operational, expected to be in 2021.
The financing includes 300 million US dollars (£242m) gleaned from Hancock Prospecting, the firm controlled by Australian mining billionaire Gina Rinehart.
Sirius will fire the starting gun on construction in January and, once completed, the mine will produce polyhalite, which can be used as a fertiliser.
A 37-kilometre underground tunnel is to be built to take the polyhalite from the mine to a processing plant on Teesside.
Planning permission has also been granted for two further intermediate shafts at Lady Cross Plantation and Tocketts Lythe.
Redcar MP Anna Turley said: "This financing news is great for Teesside. Sirius Minerals' polyhalite project is very well supported locally and we are looking forward to seeing the start of construction.
"Sirius can become a significant business for both the area and the UK for generations to come and the jobs and investment they are bringing to Teesside are very welcome."
However, environmentalists and organisations including the Campaign to Protect Rural England (CPRE) and the National Trust have campaigned against the building of the mine.
Last year, objections to the mine were raised by a consortium of 29 campaign groups which joined forces to urge the councillors and other panel members to reject the proposals, saying the mine was a "huge threat" to the North York Moors.
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