Sonu, alias Doctor (26), was arrested from Kesho Pur Mandi's area of West Delhi, said police.
In December last year, Sonu and his associates allegedly murdered Jagat Singh whose son was also killed in 2010 by hirelings of Manoj Morkhedi gang with which Doctor is associated, police said.
Doctor was declared a proclaimed offender who had a reward of Rs 25,000 reward on him, according to police.
Based on a tip-off that Doctor would be arriving in Delhi to meet someone, sleuths of Delhi's crime branch laid a trap and arrested him on Wednesday.
Police arrested Doctor under sections 302 (Punishment for Murder) and 34 (Acts done by several persons in furtherance of common intention) of IPC apart from 25 of Arms Act.