In his rookie campaign in 1989-90, Armstrong helped the team return to the Eastern Conference Finals with a 55-27 record. In 1990-91 he helped them win their first NBA title with a 61-21 record. In 1991-92 Armstrong averaged double-digit scoring while still coming off the bench behind Paxson to help the Bulls win 67 games and their second straight title. In 1993 he locked down the starting point guard spot and contributed to a 57-25 record and the Bulls' third straight title.
In 1994 he emerged as more of a leader in the wake of Michael Jordan's retirement, placing third on the team in scoring and earning his first all-star game berth while leading the team to a 55-27 record and a second-round exit from the playoffs. Armstrong finished third in scoring again in 1995 as the Bulls posted a 47-35 record, and with Jordan, Scottie Pippen and Toni Kukoc led the team to the second round again.
Selected first overall by the Toronto Raptors in the expansion draft in 1996, Armstrong moved from Toronto to Golden State to Charlotte to Los Angeles, until he landed back with the Bulls in their post-dynasty rebuilding years. After retiring, he was made personal assistant to Jerry Krause, and was a finalist to succeed him when Krause retired following the 2002-03 season.