Saim Ayub represents the Pakistan national cricket team and plays domestic cricket for Karachi Whites. Ayub is a left-handed top-order batsman who also bowls right-arm off-break and right-arm medium-fast.

Ayub's cricketing journey began in Karachi, where he was initiated into the game at a young age through tape ball cricket in Gulistan-e-Johar. In February 2021, Ayub made his Twenty20 debut for the Quetta Gladiators in the Pakistan Super League (PSL). He subsequently made his List A debut for Sindh in the 2021–22 Pakistan Cup in March 2022.

Ayub's first-class debut came in September 2022 when he represented Sindh in the Quaid-e-Azam Trophy 2022/23 season. In the 2023 PSL season, Ayub showcased his talent while playing for the Peshawar Zalmi. He hit his maiden PSL half-century off 33 deliveries, drawing comparisons to Saeed Anwar, a former Pakistani cricketing great.

Ayub's impressive PSL performances earned him a spot in the Guyana Amazon Warriors squad for the 2023 Caribbean Premier League (CPL) season. He performed well in the league, contributing significantly to his team's triumph as they claimed the CPL title.

Ayub's international career began in December 2022 when he was one of three youngsters selected to join the national squad for the second Test match against New Zealand in Karachi.

In March 2023, Ayub was named in Pakistan's Twenty20 International (T20I) squad for the series against Afghanistan. He made his T20I debut in the first match of the series on 24 March 2023, marking the beginning of his international career.

Following his T20I debut, Ayub's journey continued when he was selected for Pakistan's Test squad for the series in Australia in November 2023. He made his Test debut on 3 January 2024 in the third Test match of the series, although he was dismissed for a duck in his first innings.