The lender had recently been criticised for excluding Scottish islanders, with the exception of those living on the Isle of Skye, from its lending criteria.
Alistair Carmichael, Secretary of State for Scotland, said: “The Post Office is an integral part of everyday Scottish life.
“I am delighted that residents and businesses in our island communities from Stromness to Stornoway will now be able access the same Post Office mortgage products available to those on the mainland.”