Iyer, at the age of 12, was spotted by coach Pravin Amre at the Shivaji Park Gymkhana. Amre trained him in his early cricketing days. Iyer's teammates at the age group levels used to compare him to Virender Sehwag. He pursued his graduation from Podar College in Mumbai, where he helped his college team lift some trophies.

His junior and age-group cricket journey has been documented in the short-film title 'Shreyas Iyer Documentary – A Father's Dream' directed by cricket writer Aayush Puthran.

In 2014 Iyer represented Trent Bridge Cricket Team during a trip of the U.K., he played three matches scoring 297 runs at an average of 99 with a highest score of 171, a new team record.

Iyer made his List A debut for Mumbai in November 2014 playing in the 2014–15 Vijay Hazare Trophy. He scored 273 runs in that tournament at an average of 54.60. He made his first-class cricket debut in December 2014 during the 2014–15 Ranji Trophy. He scored a total of 809 runs in his debut Ranji season at an average of 50.56 including two centuries and six fifties. He was 7th highest scorer of 2014–15 Ranji Trophy.

In the 2015–16 Ranji Trophy, Iyer scored 1,321 runs during the tournament including four centuries and seven fifties at an average of 73.39, becoming the top scorer of the Ranji season and second player to score 1,300 runs in a single Ranji Trophy competition. In the 2016–17 Ranji Trophy, Iyer scored 725 runs including two centuries and two fifties at an average of 42.64. He scored 202 not out off 210 balls, against the visiting Australia team in a 3-Day Practice match in Mumbai, his highest first-class score.

In September 2018, Iyer was named as the vice-captain of Mumbai for the 2018–19 Vijay Hazare Trophy tournament.

In February 2015, Iyer was signed in the 2015 IPL players auction by the Delhi Daredevils for 2.6 crores (approximately $430,000). Thus Iyer became the highest earning uncapped player in the tournament. He scored 439 runs in 14 matches, with a 33.76 average and a strike rate of 128.36, making him the 9th most consistent player and Emerging Player of 2015 IPL.

He was retained by Delhi Daredevils in the 2018 IPL Auction. On 25 April 2018, he was announced as the new captain of Delhi Daredevils replacing Gautam Gambhir.^[13] On 27 April 2018, he became the youngest captain to lead the Delhi Daredevils team in the IPL history at the age of 23 years and 142 days during the match against Kolkata Knight Riders and was also the fourth overall youngest to captain any IPL side.^[14] On his IPL captaincy debut, Shreyas Iyer smashed an unbeaten match winning knock of 93 off 40 deliveries with 10 sixes, which was his third successive IPL fifty of the season to power DD to a heavy total of 219/5 in the first innings of the match before earning him the man of the match award.^[15] Under his captaincy, Delhi Daredevils managed to defeat KKR by 55 runs to secure only their second win of the tournament.^[16][17]

In March 2017, he was added to India's Test squad as cover for Virat Kohli, ahead of the fourth Test against Australia. He came on as a sub