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."
On his switch to the Blades, he added: "The thing that struck me was that there's real ambition here and I regard myself as an ambitious person, so it should be a good fit.
"I knew it was a big club but I didn't really realise until I came down how big a club it is.
"They get 20,000 crowds every week. We've got my first home game this weekend [against Yeovil] so that will be another milestone for me."
The striker had been linked with a pre-contract agreement with Rangers ahead of their transfer embargo being lifted in September.
Murphy said: "I know that talk went on but I don't know where it came from.
"I didn't speak to them and it was all just speculation as far as I was concerned."