Alex was elected as Member of Parliament in May 2015 and was re-elected in 2017 and 2019. 

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As a backbencher he served on the Justice Select Committee, and campaigned on issues including legal aid, the environment and cyber security. Alongside other MPs, including Richard Graham from the neighbouring Gloucester constituency, Alex successfully campaigned to raise the maximum sentence for stalking from five to ten years. 

He led a Parliamentary inquiry, together with the Children’s Society and Young Minds charities, into the impact of social media and cyber bullying on young people’s mental health.  The findings, derived from the evidence of over 1,000 young people, are still receiving national and international attention. They have led to significant progress in this area.

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In 2019, following months of campaigning - including a petition signed by 20,000 local residents - Alex successfully blocked Trust bosses' plans to shut Cheltenham's A&E, after it had been earmarked for closure. Speaking at the Despatch Box in the House of Commons, the then Health Secretary announced "In light of the extensive representations made to me by my honourable friend (Alex Chalk) made regarding the A&E in Cheltenham, I have spoken to the Chief Executive of Gloucester Hospitals Trust and I can announce that Cheltenham's A&E will remain open and that no proposals to close the A&E at Cheltenham will be part of the forthcoming consultation."

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During his time as a backbencher, Alex was Chair of the All Party Parliamentary Group (APPG) on Pro Bono and Public Legal Education; Vice-Chair of the APPG on Cycling; Vice-Chair of the APPG on Bees; Vice-Chair of the APPG on Eating Disorders; and a member of the APPG for Highways Maintenance.