Soon after accepting the role, Welsh was introduced to the players at training on Monday afternoon.
He will play an important role next season in the development of Melbourne's crop of youngsters that includes Jimmy Toumpas, Jack Viney and 17-year-old Jesse Hogan.
Welsh, 42, coached Vic Metro between 2009-2012 and led the representative team to victory in the past two years. Viney was a member of the victorious Vic Metro team under Welsh in 2012.
Welsh coached the Oakleigh Chargers in the TAC Cup between 2005-2008 and was also an assistant coach at the Calder Cannons.
He coached Carlton's Marc Murphy and Sydney Swans premiership player Nick Smith at the Oakleigh Chargers. He also played 42 games for Carlton and with Dandenong in the VFA.
Melbourne was pleased to have such a well-credentialed coach in the position and was looking forward to the season ahead in alignment with the Scorpions.
"Rohan brings extensive coaching experience at both TAC Cup level and at the National Championships," Melbourne football manager Josh Mahoney said.
"He has been involved with successful teams and demands high standards from his players, two attributes which we value highly as a club."
Welsh will be in the role on a part-time basis in a similar set up to the one involving former Demon Brett Lovett in 2012.
The Casey Scorpions had a strong season in 2012 under Lovett before tumbling out of the finals in straight sets. Lovett resigned from the position to spend more time with family and to concentrate on his business.
