James Edward Petroc Trelawny was born in Worcester but grew up in the Meneage district of the Lizard Peninsula in Cornwall and attended Helston School. He started his career with BBC Radio Devon in 1989, aged 19, as a reporter and presenter. During the First Gulf War, Trelawny was a newsreader for the British Forces Broadcasting Service, and then joined the station as a presenter in Hong Kong for a year. In 1992 Trelawny joined new radio stationClassic FM, in London, as the first presenter of the afternoon show. In 1994 Trelawny joined London News Radio where he hosted a daily three-hour news and talk show. In 1997 he co-presented the BBC GMR Breakfast Show, broadcast from Manchester, with Victoria Derbyshire. In 1998 Trelawny joined BBC Radio 3 full-time. Trelawny presented Breakfast, and subsequently In Tune, and has introduced hundreds of broadcasts for the station, many from the BBC Proms, as well as the Cardiff Singer of the World and the Leeds International Piano Competition. He had also broadcast for RTE Lyric FM in Ireland, where his major documentary seriesMax and St Magnus – An Orkney Saga won an ESB Media Award. Trelawny is a regular television presenter of classical music programmes for BBC Two, BBC Four and Sky Arts. As a writer Trelawny has regularly contributed to The Spectator, The Irish Times, The Catholic Herald and BBC Music Magazine. Trelawny is particularly fond of the operas of Britten and Mozart, the symphonies of Shostakovich and Beethoven's piano sonatas. He has also written blogs for the Daily Telegraph and for the BBC Radio 3 website. In May 2012 Trelawny featured in the international news after being arrested in Zimbabwe while hosting a charity music festival in Bulawayo. He was presenting a concert to raise funds for a children's charity. Immigration officials claimed he was in the country without a work permit. There was widespread international condemnation in the media following his arrest. He was not, in fact, working but giving his services free of charge. Whilst in detention he slipped and injured his shoulder. All charges were later dropped, but the Zimbabwean immigration authorities insisted that he had violated the terms of his entry visa and he was detained until a court sat to decide the outcome. He was released after a few days. In 2014, on the news that the Cornish were to be recognised as a national minority, Trelawny wrote in the Daily Telegraph: "Abroad, when I explain where I am from, the inevitable response is: 'So you are English.' 'No,' I reply, 'Cornish.' I’ll accept British, or European, but being described as English is something that rankles with most Cornishmen." On 23 August 2018, Trelawny hosted the final of Eurovision Young Musicians 2018 at the Usher Hall in Edinburgh alongside Josie D'Arby. On 5 April 2019, it was announced that Trelawny would host the Eurovision Choir of the Year 2019 alongside Swedish culture presenter at the Partille Arena, in Gothenburg, Sweden on 3 August. On New Year's Day 2020 Trelawny was the host for the BBC broadcast of the Vienna New Year's Concert.
