Dev was born as Kapil Dev Nikhanj to Ram Lal Nikhanj, a prominent timber merchant and his wife Raj Kumari Ram Lal Nikhanj in Chandigarh on 6 January 1959. His mother was born in Pakpattan, in the town of the Sufi saint Baba Farid. His father was from Dipalpur. They lived in Shah Yakka which is now in Okara district Pakistan. His four sisters were born there before partition and his two brothers in Fazilka, where they moved after partition. His father spent his early life after the partition in Fazilka. They moved to the capital city Chandigarh. Dev was a student at D.A.V. School and joined Desh Prem Azad in 1971.

Dev made an impressive debut for Haryana in November 1975 against Punjab with a 06 wicket haul, restricting Punjab to just 63 runs and helping Haryana to victory. He finished the season with 121 wickets in 30 matches.

In the 1976–77 season opener against Jammu & Kashmir, he had a match haul of 8/36 in the win. While his contribution for the rest of that season was ordinary, Haryana qualified for the pre-quarterfinals. Dev achieved his then best innings haul of 8/20 in just 9 overs in the second innings to skittle Bengal for 58 runs in under 19 overs. Haryana lost to Bombay in the quarter finals.

He began his 1977–78 season claiming 8/38 in the first innings against Services. With 3 wickets in the second innings, he took his maiden 10-wicket haul in first-class cricket, a feat he would later achieve twice in Test cricket. With 23 wickets in 4 matches, he was selected for the Irani Trophy, Duleep Trophy and Wills Trophy matches.

In the 1978–79 season, Haryana had a repeat encounter with Bengal in the pre-quarterfinal match after a lackluster season from Dev (12 wickets from 4 matches). He scored 2 half-centuries in the group stage matches. In the pre-quarterfinal match, he took a 5-wicket haul in the first innings. Poor batting by Haryana in the second innings let Bengal avenge their loss from 2 seasons back by scoring the required 161 runs for the loss of just 4 wickets. Dev stood out in the Irani Trophy match, scoring 62 runs and coming in at number 8. He took 5 catches in the game where Karnataka was defeated by the Rest of India XI. Dev arrived in the national spotlight with a standout performance in the finals of the Duleep Trophy, taking a first innings haul of 7/65 in 24 overs. He was included in the North Zone squad for Deodhar Trophy and Wills Trophy for the first time. He played his first Test match in the season against P