To win a majority, a party needed to win in 170 out of Canada’s 304 electoral districts.
The centre-right Conservatives are heading for 122 seats, a marked increase from the 95 it held before.
The Bloc Quebecois saw its support jump in the mainly French-speaking province of Quebec, the only place where the separatist party contests elections.
The group was elected or ahead in 32 seats, more than three times what the party won in 2015.
The Greens, who have criticised Mr Trudeau for not doing enough to combat climate change, also made gains on Monday.
The results could be good news for the country’s left-leaning New Democratic Party (NDP) – while the party had a disappointing night, it could exercise significant influence over Mr Trudeau’s next minority government.