Murphy impressed in his final games for the Steelmen, netting five goals as the club claimed three wins and a draw for the month.
The 23-year-old subsequently sealed a move to Sheffield United and made his debut in their FA Cup win over Oxford United last week.
Murphy was thrilled to end his Motherwell career on a high.
He said: "I won the young player of the month award once before but it's nice to win this one in my last month in Scotland.
"It was a big month for the club and I'm glad to have made a contribution.
"The results were mostly good. I wanted to leave on a high and, although we lost at Celtic Park in my last game, we had some good results and displays prior to that."