In July 2000, police were called to a Saatchi & Saatchi fundraising event, where it was alleged Ralston had punched guests. Until July 2003 he was writing for the Sunday News and the Independent business weekly, and was a talkback show host on Radio Pacific.
CEO Ian Fraser appointed Ralston head of news and current affairs at TVNZ starting on 14 July 2003, Fraser saying, "Bill's energy, his experience and just a hint of the mongrel" would meet the challenge of the job. Ralston had a goal of reducing the $46 million TVNZ news budget by $4.5 million, and there were a number of high-profile departures from the broadcaster, including Judy Bailey, Richard Long, and Paul Holmes. Discussing the departures later in 2007, he blamed the government, including Prime Minister Helen Clark, for political interference in the salary negotiations. He drew criticism in March 2005 for verbally attacking Prime Television CEO Chris Taylor, saying, "I'd be shooting myself. I'd be pouring petrol over myself and throwing myself off Auckland's tallest building". In 2006, ONE News won the Qantas Media Award Best News Programme. He faced disciplinary action also in 2006 over an expletive-laden call to a Herald on Sunday journalist, who was making enquires about a homeless cousin. Ralston resigned from TVNZ on 30 January 2007, prior to an announcement of restructuring.
Since TVNZ he has written columns for the New Zealand Herald, Herald on Sunday, The Listener, the Media Scrum blog for Fairfax Media, and in 2009 was an afternoon host for Radio Live. Former foreign minister Winston Peters refused to appear on the Sky News New Zealand show covering the 2008 general election, because he objected to Ralston, the host.