Alexander Martin Sullivan (1830 – 17 October 1884) was an Irish Nationalist politician, lawyer and journalist from Bantry, County Cork.
Alexander Martin Sullivan, the second son of Daniel Sullivan of Dublin, was born in 1830 at Bantry, County Cork, the second of six sons. He was educated in the local national school. One of Sullivan's brothers was Timothy Daniel Sullivan, the Lord Mayor of Dublin from 1886-88.
During the great famine of 1846–7 Sullivan was employed as a clerk in connection with the relief works started by the government. Deeply influenced by the distress he then witnessed, he afterwards joined the Confederate Club formed at Bantry in support of the revolutionary movement of the Young Irelanders, and was the organiser of the enthusiastic reception given by the town to William Smith O'Brien in July 1848 during the insurgent leader's tour of the southern counties. Early in 1853 Sullivan went to Dublin to seek employment as an artist. An exhibition of the arts and industries of Ireland was held in Dublin that year, and he was engaged to supply pencil sketches to the Dublin Expositor, a journal issued in connection with the exhibition. Subsequently he obtained a post as draughtsman in the Irish valuation office, and afterwards as reporter on the Liverpool Daily Post.
In 1850, Sullivan became assistant-editor of the The Nation in 1855, and subsequently editor and proprietor. From 1861 to 1884, in conjunction with his elder brother, T. D. Sullivan, he made The Nation one of the most potent factors in the Irish Nationalist cause, and also issued the Weekly News and Zozimus. Called to the Irish bar in 1876, he was made Q.C. in 1881.
At the 1874 general election he was elected as Member of Parliament (MP) for Louth, but although he did not formally resign, he did not take his seat. At the general election in April 1880, Sullivan was again returned for Louth, but this time formally resigned from the Commons on 18 May 1880. However, Charles Stewart Parnell had been elected for both Cork City and for Meath, and chose to sit for Cork. At the resulting by-election on 20 May 1880, Sullivan was returned unopposed to fill the vacancy in Meath, and held that seat until his resignation on 3 February 1882.