His best result was fourth in the South Garda Winter Cup, finishing behind Yannick de Brabander, António Félix da Costa and Robin Frijns.

In 2009, Tincknell remained with the newly renamed CRS Racing, to contest a full season of Formula Renault UK.

After a difficult weekend at the Croft circuit, he bounced back to take a pole position and victory at Snetterton breaking the lap record which still stands on the way to the win.

However, the final 4 rounds of the season proved a struggle for the team with the new Formula Renault car and Tincknell managed one more podium and 3 top five places to eventually finish 5th overall in the championship.

[11] After a tough start to the year at Monza he claimed in his first F3 podium at Oulton Park at the second race of the season before going on to finish 2nd at the next round at Snetterton.

At the following round at Brands Hatch Grand Prix Circuit, Tincknell took his first win of his Formula Three career leading the race from pole position.

After impressing in initial testing Tincknell suffered a freak accident at the Circuit de Spa-Francorchamps in Belgium, breaking his right hand severely which needed to be operated on back in the UK.

[13] Tincknell then scored another 3rd place and fastest lap at Brands Hatch before the championship combined with the Formula Three Euroseries meeting at Norisring.

[14] On his debut at the notoriously difficult Guia Circuit, Tincknell had an outstanding weekend, qualifying 7th overall and finishing 6th in the Qualification race in the 30 strong world class field.

The five-time Formula Three race winner continued his relationship with the team and has been joined by Canadian racer Nicholas Latifi and British rookies Jann Mardenborough and Jordan King.

It was the first time the 21-year-old from Devon has scored maximum points in the championship and was also a landmark victory for the Carlin team that runs his Volkswagen-powered Dallara – it was the squad's first-ever success in a non-reversed-grid race on the series' control Hankook tyres.

[21][22] Tincknell claimed his second FIA Formula 3 European Championship podium finish of the season after a strong performance in the latest round at Brands Hatch on 18–19 May 2013.

He signed with JOTA Sport to race a Zytek Z11SN-Nissan in the European Le Mans Series and finished 2nd in the 2014 ELMS Driver's Championship (74 points total) with Simon Dolan and Filipe Albuquerque after 1 win, 3 podiums and three personal poles.

In 2015, Harry re-signed with the British Jota Sport outfit in when the factory Nissan NISMO LM P1 team opted to delay its race programme.

He subsequently finished 3rd in the ELMS Driver's Championship (89 points total) driving a Gibson 015S-Nissan (formerly designated the Zytek Z11SN-Nissan) with Dolan and Albuquerque again in the five-race series, after 1 win, 4 podiums, 2 personal poles, three front row starts and two fastest race laps.

In 2016 he returned to the European Le Mans Series with Jota Sport (rebranded G-Drive Racing) Gibson-Nissan, teaming up once again with Simon Dolan and new signing Giedo van der Garde.

He won the ELMS Driver's Championship with 2 wins and 4 podiums, taking a dramatic victory at the Estoril circuit in Portugal to clinch the title by 7 points.

[26][27] When the race programme was delayed, Tincknell competed in the Six Hours of Spa-Francorchamps with Jota Sport once again and won—setting the fastest time in the LMP2 class.

[33][circular reference] During the first round of 2018–19 season Tincknell had a major accident at the Six Hours of Spa race after a front end mechanical failure caused a head on impact with the tyre barrier at the famous Eau Rouge corner.

Alongside fellow Brit Alex Lynn and Belgian Maxime Martin, the trio won the GTE Pro class by 1 minute 33 seconds.

[35][circular reference] For 2022, he joined the Dempsey-Proton Racing team alongside fellow Brit Sebastian Priaulx and German Christian Ried.

He scored Mazda's first win in 7 years at the 2019 6 Hours of Watkins Glen and won again at Road America alongside teammate Jonathan Bomarito.

They also finished on the podium[43] at Mosport having led the majority of the race, but an issue fitting the right rear tyre in the final pit stop dropped them to 2nd.

In 2024, he ran the full season in the Ford Mustang GT3 alongside Christopher Mies and Mike Rockenfeller, the team scored 2 podiums at VIR and Indianapolis.

Away from the race track, Tincknell enjoys playing golf, darts,[61] rugby, and chess, as well as supporting Plymouth Argyle, his local football club.