The proposal is conditional on Macarthur not proceeding with a proposed $766m takeover of Noble Group’s Gloucester Coal.
Macarthur earlier agreed to buy a 25% stake in the Middlemount coking venture in Queensland.
Macarthur said Peabody’s bid undervalued its growth prospects.
Noble Group, however, said it may exercise its option to increase its stake in the Middlemount mine to 50%, which would give it the right to sell 100% of the output for the life of the mine.
Peabody, which already owns eight Australian mines, wants to acquire Macarthur to increase its ability to market pulverised coal to Chinese steel producers.
Macarthur is the biggest maker of pulverised coal.