The former Hibernian and Scotland defender, who quit as Dumbarton boss to take up the post at Paisley, replaces Gary Teale after he failed to preserve their place in the Scottish Premiership.
St Mirren will begin life in the Championship next season and 34-year-old Murray, who took over at Dumbarton in November 2012, is under no illusions as to the task in hand.
Speaking to Sky Sports News HQ he said: “It’s a big challenge but it is a fantastic one as well. The club has suffered a bit of a setback recently but we are looking to bounce back instantly.
“It’s a tough league, there is no question about that and every team that has had the experience of the Championship will say that.
“Rangers and Hibs found it particularly hard this season as you have good sides in here. Falkirk, Queen of the South and if you add in Alloa and Dumbarton and the part-time teams you have a tough league there.
“I’ve said to people all along you underestimate this league at your peril and if you do that and disrespect it you will find yourselves down here for a long time.
“Promotion is the target but there is no question it will be tough. There are a number of teams who will be targeting the Premiership and we are no different. We need to be challenging to get up there.”