The Great Ship Co was liquidated in Dec 1863 and the ship taken over by the Great Eastern Steamship Co in Feb 1864. In Jul she was towed to Sheerness to be fitted out as a cable layer, during which her fourth funnel and associated boiler were removed. Chartered to the Telegraph Construction and Maintenance Co, she departed the Medway 4 Jun 1865 on her first cable laying between Valentia and Newfoundland, but the cable snapped after 1,000 miles and the attempt was abandoned. Next year, from 13-26 Jul 1866, a cable was laid successfully -- the first usable Transatlantic cable, since the first one laid in 1858 had failed after only a few weeks.
In 1867 she returned to service as a passenger ship between New York and Brest on the occasion of the Paris World Exhibition. In 1869 she laid undersea cables from France to the USA and from Aden to Bombay. Thereafter she was laid up for seven years in Milford Haven. In 1886 she was chartered for use as a floating exhibition in Liverpool, Dublin, and Greenock. Sold for breaking up 1887, which was not completed until 1891.
Well ahead of her time, the Great Eastern was at least five times larger than the next largest ship then afloat, and would not be exceeded in length until the Oceanic of 1899.