The result ends a long drought for the Danes, who last advanced to the knockout stage in 1995.
After defeating China 6-1, England topped Group D and face Nigeria in Brisbane on Monday, while runners-up Denmark meet Australia in Sydney.
"I'm so proud of the girls and of the team that we made it through the group stages, it's been a long time since a Danish team did that in a World Cup," Harder told reporters.
Denmark started with a bang and remained undeterred after a third-minute goal by defender Simone Boye was ruled offside by VAR.
Haiti end their first World Cup campaign winless from three games.
Persons:
Pernille, Luisa Gonzalez PERTH, Pernille Harder, Danes, it's, Harder, Simone Boye, Dayana Pierre, Louis, Signe Bruun, Kerly Theus, Sanne Troelsgaard, I'm, Nicolas Delepine, Joel Dubber, Christian Radnedge
Organizations:
Soccer Football, FIFA, Haiti, China, England, Australia, Bayern, Thomson
Locations:
New Zealand, Haiti, Denmark, Perth, Australia, Nigeria, Brisbane, Sydney, Danish, Bayern Munich