Day, who was quick to praise his Management team upon receiving the accolade, guided Boro to six wins out of a possible seven throughout a busy March.
Victories over Welling United, Bath City, Worthing, Aveley, Dover Athletic and Weston-super-Mare have seen The Yellow propel up The Vanarama National League South table.
Farnborough scored 16 goals across the seven games, keeping three clean sheets and a rare home defeat at the start of the month was at the hands of Champions-elect Yeovil Town.