Captain Rostron won wide praise for his energetic efforts to reach the Titanic before it sank, and his efficient preparations for and conduct of the rescue of the survivors. He was awarded a Congressional Gold Medal by the U.S. Congress, and after World War I was appointed Knight Commander of the Order of the British Empire. He was made the Commodore of the Cunard fleet before retiring in 1931.
In 1887 Rostron joined the barque Red Gauntlet as a second mate. Soon after, he left the Waverly Line and joined the barque Camphill. In December 1894 Rostron served on board the steamship Concord where he passed the extra master's certificate. He joined the Cunard Line in January 1895 and earned a position as fourth officer on the ocean liner RMS Umbria. In the years afterward he would also serve on other Cunard ships including the Aurania, Etruria, Servia, Cherbourg, Ultonia and Saxonia. Rostron was made first officer of the RMS Lusitania in 1907, but was transferred to the Bresica and made the ship's captain the day before the Lusitania's maiden voyage. The Bresica and his next several ships served the Mediterranean region, including his first passenger ship, the Pennonia, whose New York - Mediterranean route he took command of in 1911.
As a member of the Royal Naval Reserve, Rostron temporarily left the Cunard Line to serve with the Royal Navy during a period of international tension occasioned by the Russo-Japanese War of 1904 - 1905. He subsequently returned to the Cunard Line and was given command of the passenger liner RMS Carpathia.
Rostron immediately ordered the ship to race towards the Titanic's reported position, posting extra lookouts to help spot and maneuver around the ice he knew to be in the area. About 50 nautical miles (93 km) separated the Carpathia from Titanic's position, but the Carpathia was the closest ship to respond to Titanic's distress signal. Rostron and his engineering crew skillfully obtained the maximum speed possible from the Carpathia, coaxing her up to 17.5 knots - three and a half more than she was rated for. Even so, Carpathia travelling, through dangerous ice floes, took about 3½ hours to reach the Titanic's radioed position. During this time Rostron turned off heating to ensure the maximum amount of steam for the ship's engines and had the ship prepared for the survivors; including getting blankets, food and drinks ready, and ordering his medical crew to stand by to receive the possibly injured survivors. Altogether, a list of 23 orders from Rostron to his crew was successfully implemented before Carpathia had even arrived at the scene of the disaster.
When Rostron believed he was getting close to the Titanic, he had green starburst rockets launched to encourage the Titanic if she was still afloat, or her survivors if she was not. Carpathia began picking up survivors about an hour after the first starburst was seen by those in the lifeboats. The Carpathia would end up rescuing 712 survivors out of the 2,208 passengers and crew on board the Titanic; at least one survivor is said to have died after reaching the ship. After consulting with White Star Line managing director and Titanic survivor J. Bruce Ismay, Rostron decided to turn the ship around and return to New York City to drop off the survivors.
Later, Rostron testified about the events the night Titanic sank at both the U.S. Senate inquiry and the British Board of Trade's inquiry into the disaster. Titanic survivors, including Margaret Brown, presented Rostron with a silver cup and gold medal for his efforts the night Titanic sank. He was also awarded the Congressional Gold Medal, the Thanks of Congress, the American Cross of Honor, a medal from the Liverpool Shipwreck and Humane Society and a gold medal from the Shipwreck Society of New York.
In September 1915, Rostron joined the RMS Mauretania and in April 1916 he joined the Ivernia in the Mediterranean Sea. He returned to the Mauretania in 1917 before taking command of the Andania, Saxonia, Carmania and the Mauretania again. In December 1918, he was made captain on the acting list of the Royal Navy Reserve and made a Commander of the Order of the British Empire in 1919.
Rostron continued to command the Mauretania after it returned to normal passenger service in June, 1919 and in 1926 he was made a Knight Commander of the Order of the British Empire. In July, 1928 Rostron took command of the RMS Berengaria and became the commodore of the Cunard fleet.
After his retirement in May 1931, Rostron was a member and captain of the Southampton Master Mariner's Club and wrote an autobiography called Home from the Sea.
When his former ship, the much-beloved Mauretania, sailed for Scotland to the shipbreakers in 1935, Rostron was supposed to have been on board; however, overcome with emotion, he refused to board her and instead waved farewell from pierside.