After graduating from Dartmouth College Coughlin moved to New York City and worked as a composer for several years, primarily writing incidental music for plays and dance.

Coughlin has also provided additional orchestrations for the Broadway musicals Big Fish, On the Twentieth Century (2015 revival) and Something Rotten!, among others.

For Frankel and Korie, he orchestrated Grey Gardens (for which he received a Tony Award nomination), Far From Heaven, Happiness (directed by Susan Stroman), Finding Neverland (UK version) and War Paint.

He co-orchestrated (with the composer) three major Gordon operas (The Grapes of Wrath, 27 and Morning Star) and (as sole orchestrator) three musicals.

[24][25][26] In the non-theater realm, he has written orchestrations for many singers (for both concert and recording) including Audra McDonald, Kristen Chenoweth, Julian Fleisher, Nadine Sierra, and Darius de Haas.

In 2016 they collaborated once again on one of Tilson Thomas's own compositions (Four Preludes on Playthings of the Wind) with Coughlin supplying orchestration assistance as the score was finalized.

[30] It was Tilson Thomas who suggested Coughlin to Bruce Hornsby who was assembling a concert suite of four songs to be premiered at the New World Symphony in 2015.

[32] In 2019 he joined forces with Metallica and Michael Tilson Thomas and the San Francisco Symphony to create arrangements and orchestrations for S&M2, marking the 20th anniversary of the legendary S&M concert of 1999.

He also wrote a new orchestration for Master of Puppets from the original S&M concert and adapted and reworked Geoff Alexander and Michael Kamen's Enter Sandman chart.