He is also a native of St. John's, Newfoundland, Hallett co-founded Great Big Sea in 1993, with Alan Doyle, Sean McCann, and Darrell Power.

[1] Hallett is a vocal proponent of talent development within the Newfoundland and East Coast Music Industries, and has authored a career guidebook for aspiring musicians.

[citation needed] Hallett currently plays accordion and other instruments in the band Kelly Russell and the Planks; he has also been associated with The Once, The Dardanelles, Fabian James, and the Irish Descendants, in various capacities.

A founding member of Great Big Sea, Hallett performed vocals, mandolin, mandola, bouzouki, banjo, fiddle, guitar, whistles, bagpipes, accordion, and concertina with the band.

[4] Hallett, Darrell Power, and Séan McCann began playing together in a Celtic band called Rankin Street in 1989, with Alan Doyle joining in 1993.

[10] Set in the week following the September 11 attacks, the musical tells the true story of what transpired when 38 planes were ordered to land unexpectedly in the small town of Gander, Newfoundland and Labrador, as part of Operation Yellow Ribbon.

[18] In late 2005, Great Big Sea released its first podcast, with clips of the band bantering back and forth in the studio mixed with various songs by them and other artists.

[19][20] In 2016, Hallett successfully campaigned to halt Walmart sales of Saint Patrick's Day T-shirts that featured a racial slur considered offensive to native Newfoundlanders.