Robin Toskin and Reuters
While it is a personal feat for the 20-year-old midfielder, it also ends the three-year reign of Glasgow rivals Rangers, who were deducted 10 points in February for entering financial administration.
And as Glasgow erupts into wild celebration, Mugubi will reflect on a journey that started at Kamukunji via AFC Leopards and Germinal Beerschot (Belgium) before making his move to Scotland last year.
"I am very happy for Mugubi," her mother, Mildred said. "He is hard working boy. When he gets to the field of play he plays with one heart.
"I want to thank the Scots and Celtic supporters and everyone involved with the club for the way they received Mugubi.
"It was heart-breaking too see him sent off a week ago but this victory now washes away the tears of disappointment.
"I fasted ahead of the match, praying that Mugubi and his teammates win the Scottish title. Iâm happy that even if he didnât play against Kilmarnock his teammates did enough for him and the club," Mugubiâs mother told FeverPitch.
Left back Charlie Mulgrew scored twice and set up Glenn Loovens and Gary Hooper for two more before Joe Ledley and Hooper added the gloss as Neil Lennon's side gained revenge on Kilmarnock for last month's League Cup final defeat.
Celtic, also in the semi-final of the Scottish Cup against Hearts next weekend, lead Rangers by an unassailable 21 points with their bitter foes having six games left including a home match with St Mirren later on Saturday.
Celtic's next home game is against Rangers but it has already been decided they will receive the league trophy on another occasion in order not to inflame tensions.
The "Hoops", who will enter the Champions League third qualifying round next term, could have won the title at Rangers last month but a 3-2 win for Ally McCoist's side at least gave the home fans a modicum of cheer.
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