He then went on to play for Hartlepool United, Stevenage, Plymouth Argyle, Bristol Rovers and Blackpool and in August 2017, he signed for Motherwell, initially on loan, making the move permanent in January 2018.

In 2020, Hartley joined Indian Super League side Jamshedpur before returning to Hartlepool United for his second spell with the club in 2023.

[7] He made his debut for Chesterfield a day after signing, on 23 February, playing the whole match as the club secured a 1–0 victory over Brentford.

[17] In a 2–1 win over Oldham Athletic on 2 January 2010, Hartley was then sent-off in the 83rd minute after he attempted to headbutt Sean Gregan in an off the ball incident.

[29] In a 1–1 draw against Leyton Orient, Hartley was the victim of mistaken identity after he was booked by the referee, when in fact Evan Horwood had committed the foul.

[45] Hartley made his Stevenage debut on 17 August, playing the whole match in a 1–0 home defeat to Leyton Orient.

[46] After making eleven appearances for the club so far, Hartley scored his first goal, "nodding home" for Stevenage to take the lead, in a 2–0 win over Crawley Town on 26 October 2013.

[50] Then in the third round of the FA Cup, Hartley scored his second goal for the club when he headed in to make 2–0, in a 3–2 win over Doncaster Rovers on 4 January 2014.

[53] In June 2014, Hartley agreed to sign for League Two side Plymouth Argyle as of 1 July after his release from Stevenage.

[54] On joining Plymouth Argyle, Hartley quoted on the move,"I spoke to the manager a couple of weeks ago now and I was taken in by his desire to want to go places with this club.

[56] Hartley made his Plymouth Argyle debut on 17 August, playing the whole match in a 1–0 home away to Cambridge United, where he was in a central-defence partnership with Curtis Nelson.

[61] Ahead of the match against Dagenham & Redbridge, Hartley was expected to be captain in Nelson's absence,[62] however, he was dropped from the first team after suffering a hip problem during the warm up.

[63] Hartley made his return in the first team against York City, but only played for 45 minutes, suffering a hip problem for the second time.

[64] Following his return against Hartlepool United on 31 January 2015,[65] Hartley scored his fourth goal of the season, in a 2–0 win over Wycombe Wanderers on 10 February 2015.

[66] In his first season at Plymouth Argyle, he made forty-six appearances and scored five times in all competitions, Hartley signed a new contract with the club despite interest from Scottish Premiership side Ross County.

[74] On 2 January 2017, Hartley suffered a foot injury in a 4–1 defeat to Charlton Athletic and despite playing the match, was ruled out for 3 months.

[78] On announcing the signing, the club released a video parodying the unveiling of Alexis Sánchez by Manchester United earlier in the month, where Hartley plays a miniature piano and is presented with the hashtag "#Pete6".

[79] Ahead of the 2018–19 season, Hartley was named captain of Motherwell, replacing Carl McHugh who chose to step down from the position.

[93] In August 2023, Hartley moved back to India when he signed for newly formed I-League side Inter Kashi.

In July 2024, Hartley alongside Matthew Dolan formed their own company which runs football coaching summer camps.

[96] On 2 October 2024, Scottish Premiership side St Mirren announced that Hartley had joined the club as Head of First Team Transition and Loan Pathways.