Rejoining the Islanders for the 1984-85 season, he was put on a line with Brent Sutter and Clark Gillies, and scored 9 goals through the first three rounds of the playoffs, becoming a big contributor in the Islanders' drive for their fifth consecutive Stanley Cup.

Although he never emerged as a top scorer, Flatley did become a highly effective role player, adding smart positional play, strong defense, and grit to the Islanders teams in the late 1980s and 1990s.

Flatley was sometimes referred to as "the chairman of the boards" because he rarely failed to dig the puck out in battles in the corners.

[7] Flatley was a member of the University of Wisconsin–Madison NCAA Men's Ice Hockey Championship team of 1983, and national finalist of 1982.

[3] His niece, Shannon Flatley competes for the Brown Bears women's ice hockey program.