Keogh first became a member of the Assembly in 1860 to succeed Independent Thomas H. Eviston in representing the 3rd Milwaukee County district ; and was assigned to the standing committee on enrolled bills. He was re-elected for 1861, and was assigned to the standing committees on incorporations, on privileges and elections, and on ways and means; and to the joint committee on printing. For 1862, he was elected to the Senate for the Sixth District, becoming the youngest member of that body at the age of 28. He was assigned to the committees on legislative expenditures, on internal improvements, and on engrossed bills. He was re-elected for 1863, and returned to the joint committee on printing as a Senate member. He was succeeded in the Senate in 1864 by fellow Democrat Hugh Reynolds.
After the Senate
In 1867 he established his own printing company as the senior partner in the firm of Keogh & Schroeder. According to his official biography of 1876, "He twice received the Democratic nomination for the Assembly in the first ward of Milwaukee, but 'was beaten through railway influence' by a small majority at each election". One of these was presumably the election of 1869, which he lost to RepublicanStephen Harrison by 45 votes. In 1875, he was again elected to the Assembly from his old district, with 583 votes to 339 for James McGrath, who had served several terms as a Democrat but had become an Independent. He returned to the committee on incorporations, and was put on the joint committee on apportionments. He was re-elected in 1877 ; and 1878. In 1879 he defeated a fellow Democrat, ex-Assemblyman and Senator Patrick Walsh; was unopposed in 1880; in 1881 received 1043 votes to 396 for Republican J. M. Connolly; in 1882 polled 695 votes to 61 for Republican B. Farrell. In 1882 he ran for the Seventh District Senate seat that had been held by Republican Edward B. Simpson, which included his own Third Ward and another which had been in his old Senate district; he lost to Republican William Stillman Stanley, Jr., who received 2449 votes to 1662 for Keogh and 1655 for another Democrat, John S. George. His Assembly seat was taken by fellow printer Michael P. Walsh, President and nominee of the Milwaukee Trades Assembly, a labor federation which was an antecedent to Wisconsin's Union Labor Party.
Again in the Assembly
In 1886, he reclaimed his old seat in the Assembly, which had been held for two terms by Michael Walsh, with 703 votes to 308 for Populist P. J. Reilley and 206 for Republican R. G. Owens. He was re-elected in 1888, with 1,177 votes to 429 votes for Edward J. Kelly, of the Union Labor Party; and in 1890, by 962 votes, to 85 for Republican William Gunnis. Milwaukee County assembly districts were all changed before the 1892 election; Keogh was elected to the new 1st Milwaukee County district, drawing 1,698 votes to 1,420 for Republican Albert E. Smith and 40 for Populist Charles Hambitzer. Keogh was elected speaker of the Forty-First assembly on January 10, 1893. He was not a candidate for re-election in 1894, and was succeeded by Republican Henry Schooley Dodge.
