The phased deal with thyssenkrupp Materials Trading will span 10 years with a five-year extension.
COO of Germany-based thyssenkrupp Jorg Glebe said the partnership was part of its activities to expand its high-quality graphite supply sources outside of China.
NextSource is targeting April 2022 for commissioning Molo.
It said as Molo's initial production was expected to be 17,000 tonnes per annum, thyssenkrupp would receive a minimum 7,300tpa during phase one, building to 35,000tpa in phase two.
"This executed offtake agreement for the sale of our SuperFlake graphite was the culmination of a multi-year process and is yet another significant milestone in the company's strategy in becoming a graphite producer of consequence," president and CEO Craig Scherba said.
The build is funded thanks to the recent strategic US$29.5 million investment by former Xstrata CEO Davis' Vision Blue Resources.
Vision Blue now holds about 48% of NextSource on a partially diluted basis.
Davis has said Vision Blue's intent was to help NextSource become a major battery materials producer.
NextSource shares (TSX: NEXT) had leapt from below C$1 to a peak of $5.30 following the February news of the Vision Blue investment.
They gained 21.9% to close at $3.78 yesterday, valuing it at $366.7 million (US$302 million).