John Macneill trained at the (Royal) Central School of Speech & Drama on the three-year acting course. Upon graduation, and after an appearance at the Edinburgh Fringe, he joined Bedside Manners to play Bob Cratchet in A Christmas Carol, a small-scale musical tour of community venues in London. As an associate director of the company, John acted in, wrote and/or directed a further ten productions with the company, which ultimately toured to venues nationwide, including The West Yorkshire Playhouse, The Barbican Centre, and The Lyric Hammersmith. He appeared in Buddy and She Loves Me in the West End, as Tony in West Side Story at the National Theatre of Kenya, and has worked in various scales of theatre all over the UK. In 2002 he became Kneehigh's admin and marketing co-ordinator, then as co-director of Mundic Nation, he played Jack in Hell Fire Corner co-produced with Hall for Cornwall. John also played Pilia Borza in Barabas (Marlowe's Jew of Malta) and Helyar Jan in Never Say Rabbit in a Boat by Nick Darke at HfC. He played Rooster in Jerusalem touring outdoors for Common Players with Exeter Northcott. He played two shows back-to-back at the 2023 Edinburgh Fringe: Polko, and award-winning The Interrogation. A South West tour of one-man play The Coastguard in which he played Peter, received a five-star review.

Television work includes Black Books, The Bill, Doc Martin, His Dark Materials, Beyond Paradise, and The Diplomat, as well as numerous commercials, while John is probably best known as Jacka Hoblyn in Poldark Series 2, 4 and 5.

At AMATA John has worked closely with 2nd and 3rd Year students on performance, and acting for camera since 2015. His final productions The House of Bernarda Alba (2016) and The Resistible Rise of Arturo Ui (2017) won Best Actor/Actress awards, with the cast of Ui also winning Best Ensemble Company at the AMATA festival.