In 1978, Mahar joined Tom Penders staff at Columbia as an assistant coach and freshman coach, and replaced Penders when he left for Fordham to become 18th head coach in Lions history.[3][4] In his six seasons at the helm, Mahar guided Columbia to a 70-86 overall record including two second-place finishes in 1978-79 and 1981–82. He was awarded NABC District II Coach of the Year honors in 1982 for guiding the Lions to a 16–10 season.[5] While at Columbia, future college head coaches like Seth Greenberg served under Mahar.[6]
After being fired at Columbia at the conclusion of the 1983–84 season, Mahar reunited with Penders, and joined his Fordham staff as an assistant coach from 1984 to 1986.[7][8] After not being retained when Penders took the Rhode Island job, Mahar sat out of coaching in an attempt to sue Fordham for a breach of contract.[9]
Mahar returned to coaching, joining the Fairleigh Dickinson Knights women's basketball team as an assistant coach in 1989.[10] Mahar was part of a historic season for the Knights, as the 1991-92 team captured the Northeast Conference tournament title, which was later honored in the FDU Athletic Hall of Fame.[11]
In 1993, Mahar accepted the head coaching job at Johnson State College in Vermont, where he spent three seasons as the head coach, and compiled a 44–34 record from 1992 to 1995, leading the Badgers to a Mayflower Conference championship in 1995 while also being named 1995 Mayflower Coach of the Year. Mahar ranks third all-time in wins at Johnson State.[12]
Mahar's son Matt, who played for him at Johnson State, is a college basketball coach and has served as the head coach at Chaminade and Assumption College.[15][16] His younger son Eamonn is currently an assistant coach at Bryant.[17]
National champion
Postseason invitational champion
Conference regular season champion
Conference regular season and conference tournament champion
Division regular season champion
Division regular season and conference tournament champion
Conference tournament champion
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^"Archived copy"(PDF). Archived(PDF) from the original on December 21, 2021. Retrieved March 24, 2018.{{cite web}}: CS1 maint: archived copy as title (link)