Maher began his career at Bolton Wanderers where he had been at the club since the age of ten before going onto make his first-team debut in April 2016 against Reading.
In January 2015, Maher joined Blackpool in a one-month loan and he made his League debut as a substitute for in their defeat away at Watford at Vicarage Road.
At the end of the 2015/16 season, Bolton confirmed that he would be leaving when his contract expired at the end of June and the following month it was confirmed that he had joined Bolton's close neighbours Bury on a twelve-month contract.
He scored his first goal for the Shakers against Burton Albion in an EFL Cup tie in August 2016 and went on to make fourteen appearances during the 2016/17 campaign.
During August 2017, Maher joined League of Ireland Premier Division side Galway.
Bucks boss Rob Edwards was delighted International clearance had come through for today’s game against FC United of Manchester, telling the club`s official website: “Niall is a player who has been training with us for some time while we had been waiting for his international clearance to come through.
“Niall is a great player, with a good attitude and I am delighted to be bringing him into the club for the reminder of the season”.