The National Party went into coalition, serving under Peake as junior instead of senior partner, but Vaughan did not take a ministerial portfolio, spent most of his remaining term overseas, and was defeated at the 1918 election after launching a last-minute campaign as an independent candidate.

Vaughan and Labor defeated the Liberal Union government led by Archibald Peake at the 1915 election, with 26 of 46 seats in the House of Assembly.

His government improved the education system by restructuring the department's senior bureaucracy, by extending the years of compulsory school attendance and by providing better facilities for the intellectually and physically disabled.

The government legislated to allow women to serve in the police force and as justices of the peace, while it also improved workers' access to the arbitration system and diminished the court's punitive powers against trade unions.

Vaughan spent the last months of his term on a speaking tour of the United States, at the invitation of President Woodrow Wilson.

[5] He made a last-minute decision to recontest his seat the 1918 election as an independent, while still overseas – despite having formally been leader of the National Party until that point.