He was born in County Monaghan and was educated there.[1] In 1850, he married Elizabeth Rutledge. Mawhinney came to Manitoba in 1873.[2] In 1885, he was elected Provincial Grand Master for the Orange Order. Mawhinney was defeated by Kenneth McKenzie when he ran for reelection in 1886.[1] He died at Victoria, British Columbia in 1913.[1]