Pedro Cosio Masden was a Uruguayan politician and diplomat.
In 1910 as Candidate of the Colorado Party (Uruguay) he was elected 24th legislative period as representative of the Department of Montevideo in the Chamber of Representatives of Uruguay from 15 February 1911 to 27 March 1913.
From 1913 to 1916 he was Minister of Public Works.
In 1916 he was Minister plenipotentiary in Madrid.
From 1917 to June, 1918 and from 1932 to 1933 he was Minister plenipotentiary in London.
From June, 1918 to February, 1919 he was Minister plenipotentiary in Washington, D.C..
From 1927 to 1932 he was Minister plenipotentiary in Berlin.
From 1933 to 1934 he was Minister of finance of Uruguay.