The original dimensions of the Australasian were as follows: Length over all, 360 feet (including the bowsprit); breadth of beam, 42 feet; depth moulded. 31 feet, 6 inches; tonnage, builder's measurement, 2800 tons. She was fitted with engines of the direct-acting construction, delivering 700-horse power.

She was built with three decks. On the spar-deck was a spacious poop, fitted entirely for first-class passengers. There was also a top gallant forecastle for the crew, and the usual deck-houses, sculleries, butcher’s and baker's shops, cowhouses, and such. On the main-dock was a magnificent saloon, capable of dining about 200 passengers. Alongside the saloon, and the entire length of the vessel, accommodation passengers were fitted. The lower deck was appropriated to mail-rooms, bullion-rooms, store-rooms, wine-cellars, and such.

The ship was fitted with a water-ballast tank, capable of holding 400 tons of water. This tank was made perfectly water-tight and was suitable for carrying water, coals, or other cargo. This was considered to be a very important and novel addition to this class of vessel. For filling and emptying the tank a powerful steam engine was employed, capable of throwing four tons of water per minute.

The Australasian was also equipped with Clifford's patent lowering-apparatus for boats, Cunningham's patent reefing-topsails, and lightning-conductors on Sir Snow Harris's principle. The ironwork inside at bottom was coated with Westwood and Baillie's patent cement. This was the first ship built for the European and Australian Mail Company under contract with Government for conveyance of The Australian mail. It was also one of the largest and most completely equipped merchant ships built in the UK till then.

On the trial trip which took place at Southampton, the measured distance at Stokes Bay a maximum speed of 14: 575 knots per hour was attained, and an average of four runs, two with and two against the tide, gave 13:325 knots - a result deemed highly satisfactory by all concerned. On the trial the ship drew 21 feet of water, with 1200 tons cargo on board.

The first commander of the Australasian was Captain Geoffrey Sceales. The Australasian left Southampton for Alexandria on October 12, 1857. She was intended for the station between Suez and Australia