Former England Under-21 international goalkeeper Ben Alnwick joined Norwich City on a three month loan from Tottenham on 24th July 2009 as cover for Australian keeper Michael Theoklitos whose international clearance had not come through and for Declan Rudd called up by England Under-18s and Jed Steer who had injured his back

After playing for local youth side Wylam in his native Northumberland, he was signed by Sunderland for whom he made his professional debut at the climax of the 2004/05 season when Thomas Myhre was injured. He eventually became first choice keeper at Sunderland for the 2006/7 season but after a poor start, was dropped by manager Roy Keane in favour of Darren Ward.

On 2nd January 2007, Ben signed for Tottenham for £900,000 in a deal which saw Marlon Fulop head to the Stadium of Light. In September 2007 he was loaned to League One side Luton Town on a three-month loan deal. He was recalled from Luton in October, due to an injury to Paul Robinson. However, on Monday 7th January 2008, Alnwick joined Leicester City on loan until the end of the season

After returning to Spurs, he was loaned to Carlisle on 16th October 2008 but came back after a month due to injuries at Tottenham. He made his Spurs debut in the 3-2 defeat to Burnley in the League Cup semi-final second leg.

Although called up to the England Under-21 squad in August 2006 for the game against Moldova, he did not make his international debut at this level until a year later against Romania.

Ben made his debut for Norwich in the 4-0 away win over yeovil on 11 August 2009 in the Carling Cup. Injury cut short his loan and he made just 6 appearances for City

On 14th October 2010 Alnwick joined Leeds United on loan for 28 days but did not make a first team appearance

On 4th March 2011, Alnwick was loaned to Doncaster Rovers until 9th April 2011

On 9th September 2011, Ben was loaned to Leyton Orient for a month to stand in for fellow Spurs loan man David Button, who has a shoulder injury. He made his debut the following day in the 1-1 draw at Colchester. This loan was extended and he made eight appearances for the O's.

He was released by Spurs at the end of May 2012. He joined Barnsley on 5th July 2012, signing a two year deal. He made his debut for Barnsley on 11th August 2012 in a Capital One Cup clash with Rochdale but was sent off in the 90th minute for inexplicably head-butting Ray Putterill, conceding a penalty and earning himself a red card.

Alnwick had his contract at Oakwell terminated by mutual consent on deadline day (2nd September 2013). He had made 12 appearances for Barnsley. He joined Charlton on a one year deal on 4th September 2013.

On 31st January 2014, Ben rejoined Leyton Orient on a contract until the end of the 2013/14 season. O's manager Russell Slade was in the hunt for a goalkeeper as number one Jamie Jones was sidelined with a back injury and Hull City keeper Eldin Jakupovic was recalled from his loan spell at Brisbane Road following Allan McGregor's sending off for Hull on 29th January 2014, leaving Jake Larkins as Orient's only fit senior stopper.

Alnwick made just one appearance for Orient, against Rotherham on 1st February, before being unavailable for personal reasons. He left the club by mutual consent on 24th March 2014.

After trialling with Blackpool in July 2014, Alnwick signed for Peterborough on 25th July 2014. Posh boss Darren Ferguson said: "He has got vast experience and has played at the top level. He is a good goalkeeper, good size and is excellent with his feet, which is what I am looking for, someone who can play from the back. We feel with his quality and experience he will make a big difference to us. Jimmy Walker, our goalkeeping coach, has worked with him at Spurs and Gary Breen played with him up at Sunderland and both spoke very highly of him. He is very focussed, he realises he needs to get his career up to speed and the fact he has signed a three-year contract means he has a bit of stability. He can get settled in."

He was released by Peterborough in August 2016 and signed for Bolton Wanderers on 31st August 2016. He had played 84 league games for The Posh.

On 19th April 2019, Bolton were relegated from the Championship following a 2-0 defeat to Aston Villa. It was their 14th defeat in 18 games. Having played no games for Bolton for the first half of the 2019–20 season, Alnwick decided in December to mutually agree with the club to terminate his contract with immediate effect.