Blackman grew up in the Victorian suburb of Mount Waverley, where he attended Syndal Primary School until 1959 and Syndal Technical School through year 10 in 1963. He was an avid supporter of the Fitzroy Football Club, which has since merged to become the Brisbane Lions. On leaving school (and home) at 16, he worked in a succession of occupations: customs clerk, cash van salesman for a cigarette distributor, sales representative for a perfume company, and spruiker in Myer's Bargain Basement. At the age of 22, he decided upon a career in radio.

He has worked in radio since 1969 but is probably best known for his 28-year stint as announcer and character voice-over for the Nine Network's Hey Hey It's Saturday, Australia's longest running variety show. One of his best known characters was a head on a stick known as "Dickie Knee".

In 1969, he joined 2GN Goulburn as an announcer, newsreader, copy writer, salesman, and record librarian.

In 1970, he joined 2CA Canberra where he worked in a variety of on-air shifts for 18 months until mid-1971, when he joined 3AW in Melbourne.

As evening announcer, Blackman worked with the Reverend Alex Kenworthy for a number of years on "Nightline".

In 1974, he joined 3AK where he hosted the morning show until 1975, when he moved to Sydney to join 2UE as a "floating" announcer for just three months. At TCN-9 in Sydney, he was a staff continuity announcer and daytime newsreader for National Nine News alongside his work on Hey Hey It's Saturday, which he would do "down the line" to GTV-9 in Melbourne every Saturday from an announcing booth at TCN-9.

He returned to 3AK Melbourne in 1979 to host the breakfast show until 1981. Later that year, he joined 3AW to host their breakfast show with Paul Barber. After Barber parted company with 3AW not long afterwards, Blackman was joined by former ATV-0 newsreader and staff announcer, Bruce Mansfield. This collaboration became one of the most successful combinations in Australian radio history, with 3AW breakfast topping the ratings for 5 consecutive years until 1986.

After leaving 3AW in controversial circumstances in July 1986, Blackman became part of the short-lived, ill-fated CBC Network (2UE/3AK) experiment and, in December of that year, his contract was not renewed.

From 1987 to 1990, he co-hosted a breakfast show on 3UZ (now Sport 927with Coodabeen Champions member Ian Cover and later, Wilbur Wilde.

After a 7-year hiatus from radio, in 1997 he was persuaded back to the medium as host of the 3AK breakfast show with Anna "Pinky" Pinkus and Dennis Donoghue (Lawyers, Guns & Money) as co-hosts until 2000.

In 2004, he joined MMM Adelaide and was co-host of The John Blackman & Jane Reilly Breakfast Show until December 2007.

On Christmas Eve 2007, Blackman suffered a seizure brought on by a golf ball size (benign) meningioma brain tumour.

After six hours of surgery, it was successfully removed at the Alfred Hospital in Melbourne - he has fully recovered and is now enjoying good health.

Other television shows Blackman has appeared on and announced for include Blankety Blanks, Personality Squares, The Paul Hogan Show, The Daryl Somers Tonight Show, Holiday Island, Family Feud and many others. Blackman was interviewed on ABC's Talking Heads in 2006.

[1] He has authored five books including Aussie Slang, Aussie Gags and More Aussie Gags .

He can now be heard each weekday morning between 10am-11am on 531 3GG. John told the JJ website ((http://jocksjournal.com/)) that the program consists of "light hearted banter between me and co-host Jenni Burchell along with - Gippsland and the Valley’s Widest Variety of Music”.

He is married to Cecile and has a 35 year old daughter, Tiffany.

In 2009 Blackman returned as part of the Hey Hey It's Saturday reunion specials.

In 2010 he returned to Hey Hey it's Saturday to revive his role of voiceovers.