He was born in 1950 and educated at Kelly's Private School, Cabra Road; St Vincent’s CBS Glasnevin and University College Dublin, graduating with a BA (History and Politics) in 1971. He was editor of the UCD newspaper, (as a student), from 1970 to 1972, deputy president, Students' Representative Council, UCD, from 1970 to 1971, freelance New York Correspondent for the Irish Press newspaper from 1972 to 1973, sub-editor with the Irish Press from 1973 to 1977 and reporter from 1977 to 1978. He joined the Irish Times in 1979, becoming Environment Correspondent in 1986, a post which he held until he was appointed Environment Editor in 2000. He lives in the Temple Bar area of Dublin.

McDonald has long complained of the noise in Temple Bar. In 2010, he admitted to hitting a female manager in the River House Hotel in Eustace Street, after becoming frustrated with the noise coming from the hotel's Mezz bar and nightclub. In a subsequent licensing case, the Dublin Circuit Court heard that complaints about the premises dated back over 15 years and the judge said they were "well-grounded". He renewed the licence on the basis that Frank Conway, the licensee, had expended considerable sums of money to prevent further "entertainment noise break-out" and said the rights of residents of Temple Bar "have to be respected".