Portugal defeated Luxembourg 2-0 thanks to goals from Bruno Fernandes in the 39th minute and Ronaldo, from point-blank range, in the 86th minute.
The reigning European champions finished second in Group B ahead of Serbia who missed out on automatic qualification after a 2-2 home draw with group winners Ukraine.
Dusan Tadic and Aleksandar Mitrovic both goals for Serbia who were denied victory when Artem Besedin equalised in the 90th minute.
Harry Kane scored again, making it goals in all eight qualifiers, as England won 4-0 away to Kosovo.
England’s emphatic win sealed top spot in Group A and a top-six seeding for the Euros.
The Three Lions finished ahead of Czech Republic in Group A, after they lost 1-0 to Bulgaria in Sofia.
Iceland finished their group phase with a 2-1 win over Moldova but had already failed to seal automatic qualification.
France and Turkey ended up ahead of Iceland in Group H and rounded out their qualifying phase with 2-0 wins over Albania and Andorra respectively.