After being elected into the first chamber of the Riksdag, Trygger gained a reputation as a good debater with deeply conservative values.

At the time of king Gustav V's last power demonstration during the "Courtyard Crisis" of 1914, Ernst Trygger was secretly a royal advisor.

In the 1924 elections the support of the Right increased, nonetheless it was Branting who got to form cabinet, after even bigger electoral gains for the social democrats.

The Minister for Foreign Affairs, Carl Hederstierna, had openly during a speech before leading Swedish journalists declared his support for an defence alliance with Finland in the event of any Russo-Finnish dispute.

This damaged Russo-Swedish relations at a sensitive point, when trade negotiations were about to be opened and fundamentally opposed the tacit principle of Swedish non-alignment.

After having served as Minister for Foreign Affairs in the cabinet of Lindman 1928–30, Trygger cut down on his political involvement and concentrated on his academic commissions.