Mr Prothero joins Galliford Try from property developer Development Securities, where he has been finance director since November 2008.
From 2001 until 2008 he was a partner with Ernst & Young, and before that he previously held positions as finance director at Blue Circle Properties and Taylor Woodrow's UK housebuilding operations.
Galliford Try chief executive Greg Fitzgerald said: "I am delighted that Graham is joining us as group finance director. Graham has considerable financial experience in the property and housebuilding sectors and accordingly he will be a valuable asset to the group as we continue to further develop the business. I would also like to express my sincere thanks to Frank Nelson on his significant contribution to the group over the last 25 years."