Graham was born on 9 September 1982 to Richard and Maureen Onions. He has an elder sister Christine. Onions attended St Thomas More Catholic School in Blaydon, and at Gateshead leisure centre he took the opportunity to try a variety of sports. He was adept at badminton and was selected for the England team at under-15 level. From playing his early cricket on the streets, Onions became part of Gateshead Fell Cricket Club. He married his wife Emma in 2010 and has two children, Oliver James (2013) and Esmé Amelia Rose (2015).

Early career

After being spotted by Geoff Cook, Durham's coach, Onions made his second XI debut for the club at the age of 18. He was offered a contract with the club and opted to become a professional cricketer rather than take a sports science choice at university, which was his other option. Onions started in the team as the fourth bowler. Looking back on his early career, he felt that he tried too hard early on. On one occasion he recalled how "I remember being thrown the ball at an important stage of a game at Scarborough, and Phil Jaques hit me for four successive fours. I was thinking 'I'm not sure I can do this.' But Dale Benkenstein was a huge influence as captain, and you have to learn from all those experiences. Otherwise I could not have done what I did in my first season of Test cricket. I often went for 15 to 20 runs in my first three overs, but always came back strongly." In 2006, Onions regularly opened the bowling for Durham with Ottis Gibson.

First international selection

On 3 September 2006, he received his first England call-up, being brought into the ODI squad to face Pakistan, following an injury to Darren Gough. However, he did not play any international fixtures. Onions was named in England's provisional 30-man squad for the 2006 ICC Champions Trophy after a successful season that year, and toured Bangladesh with the England A team under the future England coach Peter Moores. In July 2007 he was selected for the England Lions team to face the Indian tourists in a warm-up match. On 21 February 2008 Onions took 7/39 in a one-day fixture against Maharashtra, his best one day bowling figures to date.

International breakthrough

In January 2009, Onions, returning from injury, played in the losing Stockton (Newcastle) side against the Tamworth side in the New South Wales country cup competition played at the Sydney Cricket Ground. On 29 April 2009 Onions was named in the England squad for the upcoming Test series against West Indies, at the expense of his Durham team-mate Steve Harmison. He celebrated his call-up by taking 6/31 for his county against Somerset.<