On 17 November 1911, he replaced conservative Jenkin Coles as Speaker of the House; he would hold the role until the defeat of the Verran Labor government at the 1912 election.
[8] The ministry initially continued in minority government, but was ousted by the opposition Liberal Union in July.
[9] The National Party became the junior coalition partner in the new Liberal ministry under Archibald Peake, and Jackson was appointed Commissioner of Crown Lands and Immigration.
[4][12][13] Jackson died in the Royal Adelaide Hospital in 1951 at the age of 74; his family declined a state funeral, and he was buried at Centennial Park Cemetery.
[3] Upon his death, the Tattersalls Club renamed their main horse race the "Harry Jackson Handicap" in his honour.