DeGrussa produced 19,313 tonnes of copper and 13,541 ounces of gold at C1 cash costs of just US51c per pound in the June quarter.
The result took full-year production to 72,238t of copper and 42,263oz of gold at 72c/lb, beating its guidance of 70,000-72,000t of copper and 38,000-40,000oz of gold at US90c/lb.
Guidance was withdrawn earlier this year due to uncertainties relating to COVID-19, but was reinstated in May.
Sandfire managing director Karl Simich described it as an "extraordinary and pleasing result".
FY21 production is expected to be slightly weaker at 67,000-70,000t of copper and 36,000-40,000oz of gold at C1 costs of 90-95c/lb.
The company said C1 costs would move back to life-of-mine averages and grade would be slightly lower than FY20's record result.
Sandfire continued to advance its Tshukudu project in Botswana and Black Butte project in Montana, as well as maintaining aggressive exploration programs.
The company is trying to avoid a production gap when DeGrussa reaches the end of its life in 2023.
It is also progressing studies into gold tailings retreatment, as well as further gold exploration.
Unaudited revenue for FY20 was A$657 million, with the company finishing June with cash of $291 million and no debt.
Simich said the company was in a "strong and flexible position" to fund its growth.
Argonaut Securities analyst Matthew Keane maintained a recommendation for Sandfire with a revised target price of $5.90, up from $5.75.
Sandfire shares closed 5.7% lower at $5.24.