Adrian is one of many wingers (Mark Barham, Louie Donowa, Dale Gordon, Ruel Fox, Darren Eadie, Keith O'Neill) that have been produced by the club's youth team setup. Adrian made his debut in the 1-0 victory over Wolves in August 1996 and made a total of 11 appearances by the end of that season. He had made 121 appearances by the end of his spell at Carrow Road although over 40% of them were as substitute.

He was spotted by Norwich scout Colin Watts playing for West Middlesex Colts at the Canary Cup and invited for a trial although his parents couldn't see how playing football could be a job. The following year they won the Canary Cup and Watts and Gordon Bennett scouted him and invited him for trials which his parents accpeted. He signed schoolboy terms for Norwich aged 14 travelling across London to Liverpool Street to head up to Norwich on the train on Saturday nights before playing youth games on a Sunday.

Adrian was placed on the transfer list in mid August 1999 along with Darren Kenton. Although he signed a new contract in March 2001, Forbes was surprisingly transferred to Luton on 16th July 2001 for £60,000. With Nigel Worthington unable to guarantee him first team football next season, Forbes obviously saw stepping down by two footballing tiers as the lesser of two evils.After a successful 2001/02 season that saw Luton promoted from Division Three, an injury sustained during the 2002 pre-season means that Adrian will miss most of the 2002/03 season. 2003/4 was more profitable as he scored 14 goals for the Hatters

Failure to agree a new contract with Luton at the end of the 2003/4 season saw Adrain depart to Wales, joining Swansea City on a two-year contract.

The Swans released Adrian on 30th May 2006 due to the form of Leon Brittain and youngster Shaun McDonald. Adrian then joined Blackpool on 23rd June 2006

After making 36 appearances, scoring once, for Blackpool, Adrian transferred to Millwall on an eighteen month contract on 3rd January 2008

A day short of 13 months later and Forbes was loaned out to Grimsby until the end of the 2008/9 season

Adrian was one of 10 players released by Millwall on 27th May 2009 following their League One play-off final defeat to Scunthorpe. He rejoined Grimsby in early July 2009

Following Grimsby's relegation to the Conference at the end of the 2009/10 season, Forbes was placed on the transfer-list. In the summer of 2010 He trained with Darlington for a week before returning to join the Mariners on their pre-season tour to Stirling. A move to Darlington looked imminent in mid-July but the availability of the former Norwich and Millwall man has attracted interest elsewhere. "There's a couple of other clubs showing an interest in Adrian as well as Darlington," said Grimsby manager Neil Woods.

Forbes was released by Grimsby in August 2010. After a trial with Hayes and Yeading, he signed for Lowestoft at the end of September 2010, and made his debut against Wealdstone on 2nd October 2010, coming on as substitute and scoring Lowestoft's second in a 2-0 win.

An interview in the Swansea matchday programme for the game with Norwich on 8th December 2012 revealed that Forbes left Lowestoft earlier in 2012 and is now coaching at Norwich's academy. He is also the Carrow Road stadium announcer at home matches.

On 9th November 2017 Forbes revealed a battle with depression which left him in "utter despair." He follows in the footsteps of Darren Eadie, Leon McKenzie and Cedric Anselin in making his struggles public. Forbes told how he felt “lost and forgotten” when his football career came to an end, and that depression threatened to consume him. He said: “At 32, I faced the situation where I’d had nine operations on one knee, and just couldn’t carry on as a player – something I’d done for 20 years. I fell into depression and utter despair, because I just didn’t know what to do. I’d arrived here in Norwich, from a tough part of North West London, when I was just 15, so I’d made this region my life, and my sport was everything.” He said it was the business community of East Anglia which proved to be his saviour - which is why he said he was anxious to encourage more businesses to support footballers and other sporting young people. “In the end, I was so very fortunate, because businesses came forward to signpost me, and I ended up engaged with the Community Sports Foundation (the registered Norwich City Football Club Charity). As a result of that I was put forward for the Premier League Elite Coaches Apprenticeship Scheme, and eventually I found myself getting one of the two funded places for BAME (Black Asian and Minority Ethnic) coaches.

In an interview with On The Ball City for the match against Bristol City on 23rd February 2019, it was reported that Forbes is responsible for the day-to-day running of the academy, looking after the under-8s to under-11s. He had six part-time members of staff and his role also involves liaising with parents.

Forbes left Norwich's academy in April 2019. At the end of June 2019, he rejoined Luton Town as Head of Academy Coaching and Professional Player Development. He will oversee the development of players who have stepped up from youth football.