Born into a Malayali Christian family Sanju’s father, a police constable, and the family resided in the Police Quarters in Delhi. When Sanju failed to make it to the Delhi U13 team, his father took early retirement from the police force and relocated with his family to Kerala. Sanju continued his cricketing journey in Kerala and joined the U13 team of the state. A right-handed wicketkeeper-batsman, Sanju captains Kerala in domestic cricket and is a member of the Rajasthan Royals in the Indian Premier League, where he was awarded the Emerging Player of the Year. 

He was named vice-captain of the India U19 team for the 2013 Top End Under 19 Series in Australia. In the same year, he served as the vice-captain of the Under 19 Asia Cup in UAE and the Indian U-19 team for the 2014 Under 19 Cricket World Cup. He made his India debut in the 2015 T20 against Zimbabwe and his One Day International debut in 2021 against Sri Lanka.

In 2019, after four years, he was recalled to the Indian side as part of India’s T201 squad for their series against Bangladesh. In 2020, he was named in India’s T20I and ODI squad for their series against Australia. In June 2021, he was named in India’s ODI and T20I squads for their series against Sri Lanka. In 2022, he was named in India’s squad for the T20I series against England and the T20I series against West Indies.

In 2009, he was signed by Kolkata Knight Riders, and in 2013, he was signed by Rajasthan Royals. He made his debut for Rajasthan against Kings XI Punjab and won the Best Young Player Award in 2013. In 2016, Delhi Capitals signed Samson after Rajasthan was banned from competitive cricket. He returned to Rajasthan in the 2018 IPL auction. In 2021, he was named captain of the Rajasthan Royals.

Sanju is currently working as a manager at Bharat Petroleum, Thiruvananthapuram. In 2018, he established a sports academy dedicated to cricket and football training for young players in Thiruvananthapuram. He was appointed as the State Election Icon of Kerala ahead of the 2021 Kerala Legislative Assembly election. In 2023, Indian Super League Club Kerala Blasters FC appointed Sanju as its brand ambassador.