On 28 January 2012, Reinsalu became the chairman of the Pro Patria and Res Publica Union, an Estonian national-conservative, Christian-democratic political party, replacing Mart Laar.

[8][9] He was elected chairman with an absolute majority in the first round of voting at the party congress held in Tallinn.

[9] On 11 May 2012, Reinsalu was appointed minister of defence, replacing Mart Laar, who resigned from office for health reasons.

[16] He returned to the foreign ministry in July 2022, after Prime Minister Kaja Kallas dismissed her Estonian Centre Party coalition partners.

[17] On 31 March 2023 at a meeting of the Bucharest Nine Reinsalu called for the cancellation of the NATO-Russia Founding Act, because in his view cooperation with the country was "out of the question".

[19][20] In 2012, Reinsalu was criticized for endorsing Estonia's "Valentine's Day Law" that declared Estonian WW2 veterans who fought on the side of Nazi Germany (including members of the 20th Waffen Grenadier Division of the SS) "freedom fighters",[21] and for attending the meeting of the Union of Estonian Freedom Fighters (an organization of these veterans) on the island Saaremaa.