He wasKalākaua appointed him Minister of Finance on November 7, 1874, during which he was a member of the House of Nobles in the legislature.{{sfn|Lydecker|1918|p=136}} The announcement cited Walker's business success in Hawaii as the factor in his being appointed.<ref>{{cite news |title=The Re-Constructed Cabinet |url=https://chroniclingamerica.loc.gov/lccn/sn82015418/1874-11-07/ed-1/seq-2/ |accessdate=September 27, 2018 |work=The Pacific Commercial Advertiser |date=November 7, 1874}}</ref> Within the next month, Walker publicly released "Statement of the Revenues and Expenditures of the Hawaiian Kingdom for eighteen years."<ref>{{cite news |title=Taking Account of Stock |url=https://chroniclingamerica.loc.gov/lccn/sn83025121/1874-12-16/ed-1/seq-2/ |accessdate=September 27, 2018 |work=The Hawaiian Gazette |date=December 16, 1874 |page=Image 2, col. 2}}</ref> In 1876, Walker left the cabinet to work for W. G. Irwin. In 1890, Kalākaua once again named him Minister of Finance, as well as ad interim Attorney General until [[William Nevins Armstrong]] accepted the position. He remained Minister of Finance until 1882. He was appointed to the Privy Council in 1886 and named as Auditor-General. Appointed once again to the House of Nobles, he became President of the legislature, and once again in 1890–1893.{{sfn|Lydecker|1918|pp=156, 178, 182}}
During the [[Overthrow of the Kingdom of Hawaii]], Walker was the one charged with delivering the message to [[Liliʻuokalani]] that her abdication was expected by the [[Provisional Government of Hawaii]].{{sfn|Liliuokalani|1898|p=387}}
