Bostwick started his career at Millwall, and played regularly for the club's under-18 team and reserve team. At the age of 17, he joined Conference National club Crawley Town on work experience during the latter stages of 2005–06 season. On return to Millwall, Bostwick signed a new one-year contract with the club, but was sent back to Crawley Town on loan in August 2006. Bostwick played regularly for Crawley until he was recalled by Millwall in January 2007, and was told he was surplus to requirements at the club. He subsequently signed for Rushden & Diamonds on an 18-month contract, but only played eight matches before falling out of favour at Nene Park, and was released by Rushden at the end of the 2006–07 campaign.
He joined Ebbsfleet United in August 2007 ahead of the 2007–08 season, playing regularly throughout the campaign, helping Ebbsfleet win the FA Trophy at Wembley Stadium in May 2008. Bostwick rejected a contract offer from Ebbsfleet, and signed for Stevenage just ten days after the FA Trophy success. He was a regular fixture in the club's defence and midfield throughout the season, winning the FA Trophy once more in May 2009. His second season at the club was a successful one, scoring eight goals in all competitions, as well as helping the Hertfordshire club earn promotion to the Football League for the first time in the club's history. The following season, Bostwick played an instrumental part in Stevenage earning back-to-back promotions following their sixth-place finish and subsequent League Two play-off victory in May 2011. After four years at Stevenage, Bostwick signed for Peterborough United in July 2012.
Bostwick began his career as a trainee with Millwall, and was a regular in the club's Under-18 team, as well as playing several times for the reserve team. During the latter stages of the 2005–06 season, Bostwick joined Conference National club Crawley Town on work experience. The move counted as work experience, as opposed to a loan, because of Bostwick's age – subsequently he could not appear for the first team of another Football League club, but was eligible to play for the first team of a non-league club. He made his debut for Crawley a week after joining the club, coming on as an 89th minute substitute in a 1–0 victory against Forest Green Rovers. He came on in the 83rd minute in the following match against Southport at Haig Avenue, as well as playing for 25 minutes against Burton Albion, setting up Tony Scully's 89th-minute equaliser. He subsequently started his first match in April 2006, playing the whole match in a 2–0 win against Aldershot Town, scoring Crawley's second. A week later, Bostwick scored both of Crawley's goals in the club's 2–2 draw against Halifax Town, netting in quick succession to give Crawley a two-goal lead. He played a total of eight matches for Crawley during his two-month work experience, scoring three times. On return to his parent club in May 2006, Bostwick signed a one-year contract with Millwall. Shortly before the start of the 2006–07 season, Bostwick was loaned out to Crawley Town for a second spell at the club. He played in the club's first five matches of the season, scoring twice from midfield in a 3–2 away win at Stevenage. In late August 2006, Crawley Town extended the loan deal until the end of the season, although Millwall were able to recall him in the January transfer window if they deemed it necessary. Bostwick played a total of 25 times during the first half of the season, scoring twice, before Millwall recalled him in January 2007.
Bostwick returned to Millwall, but failed to make any first-team appearances. In late January 2007, he was allowed to leave the club on a free transfer to sign for Rushden & Diamonds on an 18-month contract. Rushden were managed by Graham Westley, who had previously written about Bostwick's credentials in his weekly column in The Non-League Paper when Westley was out of work. Bostwick made his Rushden debut in the club's 2–1 away win at league leaders Dagenham & Redbridge, and came off the bench in the following match against St Albans City. He was sent-off for the first time in his career in Rushden's 2–2 draw with Aldershot Town, receiving a red card for two bookable offences. Bostwick played eight matches for Rushden, but fell out of favour at the club in March 2007 after Westley was fired. As a result, Bostwick did not play for Rushden again, and was released by the club at the end of the 2006–07 season.
At the start of the 2007–08 season, Bostwick signed for Ebbsfleet United on an initial three-month contract, with a view to a contract extension after the three-month period. He was signed to add "depth to the squad", as well as to "provide cover at the back and midfield areas". He made his Ebbsfleet debut a day after signing for the club, starting the match in central defence in a 1–0 victory at Nene Park against his former employers, Rushden. He scored his first goal for the club in a 1–1 draw against Exeter City in September 2007, turning in Stacy Long's corner to give Ebbsfleet the lead. A month later, he was sent-off in the club's 3–1 away win against Altrincham for picking up two yellow cards. He returned to the first team in November 2007, assisting Stacy Long's goal in the club's 2–1 win against Stafford Rangers. Shortly before the match, Bostwick signed a new contract at Ebbsfleet, keeping him at the club until the end of the season. In January 2008, Bostwick netted Ebbsfleet's third goal in a 4–1 victory against Grays Athletic at Stonebridge Road, and scored again just four days later in another 4–1 win, this time in the 90th minute against Weymouth. He scored his fourth league goal of the season against Stevenage at Broadhall Way in March 2008, scoring with a close-range header in a 3–1 defeat. Bostwick also came off the bench on the hour mark against Farsley Celtic to assist two of Ebbsfleet's goals in a 3–1 victory – with Liam Daish saying Bostwick "changed the game". He made another assist in the club's next home fixture, a 2–0 win against Altrincham. Bostwick was also instrumental in the club's FA Trophy campaign during the season, playing in seven of the club's eight FA Trophy matches, and scoring in a 1–1 draw against Aldershot Town in the semi-final second leg. He also played the whole match in the Final as Ebbsfleet ran out 1–0 winners against Torquay United at Wembley Stadium. He made 51 appearances for Ebbsfleet in all competitions during the season, scoring five times.
Bostwick was offered a new deal by Ebbsfleet ahead of the 2008–09 season, but rejected the offer and instead opted to join Stevenage on a two-year deal, playing under the management of Graham Westley once more. He made his debut for Stevenage in the club's opening match of the season, a 5–0 defeat to Wrexham at the Racecourse Ground. Bostwick was used in both the centre of defence and the centre of midfield during the first half of the 2008–09 season, as well as playing at full back in the club's 1–0 defeat to Kettering Town in September 2008. Bostwick provided the assist for Lee Boylan's second-minute goal against Forest Green Rovers in a 3–0 victory. A month later, he scored his first goal for the club, scoring in the 80th minute against Mansfield Town to give Stevenage a 3–2 lead. He scored his second goal of the season against Weymouth in February 2009, latching onto a long pass and sliding the ball past the goalkeeper to secure a 3–0 away win. Bostwick also scored Stevenage's first in a 2–0 away win at Crawley Town, scoring with a strike from just outside the area as Stevenage finished in the final play-off spot. He subsequently played in both of Stevenage's Conference Premier play-off matches against Cambridge United in April 2009, as the club lost 4–3 on aggregate. Bostwick played in all seven of the club's successful FA Trophy campaign, as well as playing the whole match in Stevenage's 2–0 win against York City in the Final at Wembley Stadium. The FA Trophy win meant that Bostwick had won the competition in consecutive years. Bostwick made a total of 49 appearances in his first season at Stevenage, scoring three times.
Bostwick started in Stevenage's first match of the 2009–10 season, in a 1–1 draw against Tamworth, and also provided the assist for Joel Byrom's goal in Stevenage's next home fixture against Ebbsfleet United. His first goal of the season came in the club's 2–1 home win against Rushden & Diamonds, scoring from the edge of the area to give Stevenage the lead. He also provided an assist in the club's 3–2 away fixture against Mansfield Town at Field Mill, as Stevenage came from two goals down to win the match. A week later, Bostwick scored a volley away at Chester City, although due to Chester City being expelled from the league, Bostwick's goal, and subsequently Stevenage's 1–0 win, were removed from the records. Bostwick continued his goalscoring form, scoring from 25 yards after a well-worked corner in injury time, in a 4–0 win against Hayes & Yeading United. He scored a similar goal against Gateshead in November 2009, his fifth of the season. His next goal came in March 2010, scoring the opener from 30 yards against Crawley Town as Stevenage won 2–0, and he scored another goal two weeks later, heading in an Andy Drury corner as Stevenage came from behind to win 2–1 at Grays Athletic. Bostwick also played in the club's 2–0 win against Kidderminster Harriers at Aggborough in April 2010 – the match that secured Stevenage's place in the Football League for the first time in the club's history. He played in five of the club's FA Trophy fixtures during the 2009–10 season, scoring once in a match against Dover Athletic in January 2010. He also played in the Final at Wembley Stadium, but was unable to record a third Wembley victory as Stevenage lost 2–1 to Barrow after extra-time. In total, Bostwick played 52 matches in all competitions, scoring eight times. At the end of the season, Bostwick was out of contract and Westley announced that he expected him to leave, saying it would be "very difficult" to keep hold of him. However, in June 2010, Bostwick signed a new two-year deal with Stevenage, despite attracting interest from several League One clubs.
Ahead of the 2010–11 season, Bostwick scored in a pre-season friendly against Hitchin Town, and made his first league appearance in the club's 2–2 draw with Macclesfield Town, playing the whole match. He scored his first goal of the season in the club's first ever Football League victory, in a 3–1 win against Stockport County, scoring with a shot from 30 yards to double Stevenage's lead just before the interval. In November 2010, Bostwick provided two assists for Stevenage's goals in the club's 3–0 win away at local rivals Barnet. Bostwick scored his second goal of the 2010–11 season in Stevenage's 3–1 FA Cup win over Newcastle United in January 2011. Bostwick picked up a loose pass and rifled a shot that went in off the post from 25 yards out to give Stevenage a two-goal lead. A month later, he scored his third goal of the season in a 4–0 win against Cheltenham Town, cutting in from the right and drilling a low shot across the face of goal and past the goalkeeper. Bostwick played a total of 51 matches during the 2010–11 season, scoring three goals. This included three appearances in the 2010–11 League Two play-offs following Stevenage's sixth-placed finish. Following a 3–0 aggregate victory over Accrington Stanley, Stevenage earned promotion to League One after a 1–0 win against Torquay United at Old Trafford on 28 May 2011, with Bostwick playing the whole match.
Prior to the start of the 2011–12 season, Bostwick scored in Stevenage's 2–1 pre-season victory at Dagenham & Redbridge on 30 July 2011. A week later, he started in Stevenage's first ever League One fixture, a 0–0 draw against Exeter City. Three days after the draw, on 9 August, Bostwick scored his first goal of the campaign in a 4–3 extra-time defeat to Championship team Peterborough United, scoring with a 25-yard shot that took the match to extra-time. In Stevenage's next league fixture, a 1–1 draw away at Chesterfield, he was sent-off after receiving two yellow cards, resulting in a one-match suspension. Bostwick signed a two-year contract extension with the club on 26 August 2011. He scored his second goal of the 2011–12 season in Stevenage's 5–1 home win over Sheffield Wednesday, with his 25-yard half-volley rebounding off of the post and into the net to give Stevenage a three-goal lead in the first-half. Bostwick was also instrumental in the club's 6–1 away victory at Colchester United on 26 December, scoring one goal and assisting another. His goal restored Stevenage's two-goal cushion in the match on the hour mark, before he assisted Scott Laird from a well-worked free-kick routine ten minutes later. He beat his goal tally from the previous season when he scored his fourth goal of the campaign in Stevenage's 4–2 victory against Milton Keynes Dons at Broadhall Way on 24 January 2012, with Bostwick restoring parity in the first-half with a long-range strike. Bostwick also scored in a 2–2 draw against Huddersfield Town on 28 February 2012, heading in Joel Byrom's cross to half the deficit as Stevenage fought back to earn a point after being two goals down. He scored two goals in as many matches in late March 2012, both of which were long-range strikes that drew Stevenage level in matches against Walsall and Bournemouth respectively. Four days after the goal against Bournemouth, Bostwick was on the scoresheet once again, his third goal within the space of a week, scoring late-on to give Stevenage a brief lead in an eventual draw against Wycombe Wanderers. He was almost ever-present during the campaign, playing 53 times and scoring eight goals, as Stevenage narrowly lost over two legs in the play-off semi-final. During his successful four seasons with the club, Bostwick made 207 appearances, scoring 22 goals.
In July 2012, Bostwick signed for Championship club Peterborough United on a three-year contract, for an undisclosed fee. Peterborough chairman Darragh MacAnthony stated that Bostwick was manager Darren Ferguson's "number one transfer target for the summer". He made his Peterborough debut in the club's first match of the 2012–13 season, playing the whole match in a 4–0 home win over Southend United in the League Cup. Bostwick scored his first goal for the club in his fourth appearance, halving the deficit with a "stunning volley from the edge of the area" as Peterborough lost 2–1 at home to Leeds United on 25 August 2012. He was made captain ahead of Peterborough's home match against Derby County in October 2012, and opened the scoring in the match with a volley, his second goal of the season, in a 3–0 victory. Bostwick's third goal of the campaign came in Peterborough's surprise victory over table-topping Cardiff City, scoring a powerful 30-yard free-kick in a 2–1 win. He added another goal to his tally in the club's important 2–1 win over Barnsley at London Road on 1 January 2013, again scoring courtesy of a free-kick.
On 20 July 2017, Bostwick signed for newly promoted League Two club Lincoln City on a two-year contract for an undisclosed fee.
Bostwick was called up to play for the England C team, who represent England at non-league level, in a match against Italy C in Benevento in November 2008. He came on as a 56th-minute substitute in a match that ended 2–2. He was called up again to represent England C in a match against Belgium U23 at the Kassam Stadium in May 2009. However, he was forced to withdraw due to injury, and was subsequently replaced by fellow Stevenage midfielder Joel Byrom. Bostwick was called up once more to play against Poland U23 in Grodzisk Wielkopolski, but again had to withdraw due to injury.
Bostwick was born in Eltham, London and grew up in South East London. He supports West Ham United, and states that his footballing hero when growing up was Rio Ferdinand. He has one daughter, whom his partner gave birth to in 2007.As of match played 30 April 2017
Ebbsfleet UnitedFA Trophy: 2007–08
StevenageFA Trophy: 2008–09
Conference Premier: 2009–10
Football League Two play-offs: 2010–11
IndividualConference Premier Team of the Year: 2009–10