The Treaty of Perth ended military conflict between Norway under Magnus the Law-mender and Scotland under Alexander III over the sovereignty of the Western Isles, the Isle of Mann and Caithness.

In Norwegian terms the Western Isles were known as the Sudreys (meaning Southern Isles) and they had become Norwegian territory during centuries when both Scotland and Norway were still forming themselves as coherent nation-states. The treaty was agreed three years after the 1263 naval Battle of Largs and in Scotland - page 90 (Pimlico 1992, ISBN 0-7126-9893-0) - Michael Lynch compared the treaty's importance with that of the 1237 Treaty of York .

Largs is often claimed as a great Scottish victory, but the Norwegian forces, led by Hakon IV, were not fully committed to battle and the result was inconclusive. Hakon had planned to renew military action the following summer, but he died in Orkney during the winter. His successor, Magnus the Law-mender, sued for peace and secured the Treaty of Perth.

In the treaty Norway recognised Scottish sovereignty over the disputed territories in return for a lump sum of 4000 marks and an annuity of 100 marks. The annuity was actually paid during subsequent decades.