In June 2009, aged 15, Topley made the headlines when he was injured bowling in the nets at Loughborough University to England batsman Kevin Pietersen.

Pietersen flat drove a delivery, which ended up striking Topley on the side of the head, knocking him to the ground.

Following the incident, Pietersen, whom Topley cited as his favourite player, gave the youngster his cricket bat with his signature on.

[9] Mid-season Topley took a break from county cricket to return to Royal Hospital School to revise for his summer exams.

The start to his career drew praise from former England captain Michael Vaughan, who stated that Topley could become a future Test cricketer.

On 1 September 2015, Hampshire County Cricket Club confirmed the signing of Topley from Essex at the end of the 2015 season.

In IPL 2021, he was asked for being a replacement for injured Josh Hazlewood by Chennai Super Kings, but he denied the offer as the cricketer feared by the hike of COVID-19 cases in India.

[17] In 2024, he and his teammate from Royal Challengers Bangalore, Will Jacks, were withdrawn from the final stages of the IPL due to international duties.

He kept his place in the England side for the T20 World Cup, but was expensive in the first game against the West Indies, taking figures of 1–22 in 2.1 overs.

Topley was part of that successful T20 squad that was defeated in the World Cup Final in India, but upon returning home was found to have a stress fracture in his back.

In October 2021, Topley was added to England's squad for the 2021 ICC Men's T20 World Cup as a travelling reserve.