The 25-year-old midfielder scored five goals in five games for his English lower league side Rotherham United for the month under review.
Ajayi first joined his present club in 2017 on a loan deal, scoring once in seventeen appearances for them.
However, he signed a permanent deal with the Millers after the expiration of his temporary stay at the New York Stadium.
After being presented with the award on Friday, the Nigerian midfielder expressed delight with the recognition.
He added that his teammates contributed to his success all through the month.
Ajayi said: “It is a massive honour, and it is something I am really pleased to receive. I have to say though that the award is a team effort, I wouldn’t be in the position to collect the award without my teammates.
“During the month we performed well in a number of games, picking up some vital points. It was a good all round team effort. I am also hugely grateful to the staff, who have been brilliant.
“It was a good month, and to be given the award ahead of some very stiff opposition is even more pleasing.
“The season is coming to a close now, but from a team perspective we are still fighting hard to keep this club in the Championship, and from a personal point of view this will also give me confidence going into the remaining games this season.”
Ajayi made his debut for the Nigeria national team last year, and could be one of the players to feature for the team in Egypt this summer.
The 23-year-old joined the Championship side before the start of 2018 World Cup from his former team CD Feirense.
His goal came on the back of his 25th appearance for the Potters eight months after his switch last summer.