Thomas Andrews was born at Ardara House, Comber, County Down, in Northern Ireland, to The Rt. Hon. Thomas Andrews, a member of the Privy Council of Ireland, and Eliza Pirrie. His siblings included John Miller Andrews, the future Prime Minister of Northern Ireland, and Sir James Andrews, the future Lord Chief Justice of Northern Ireland. Thomas Andrews lived with his family in Ardara, Comber. In 1884, he began attending the Royal Belfast Academical Institution until 1889 when, at the age of sixteen, he began a premium apprenticeship at Harland and Wolff where his uncle, the Viscount Pirrie, was part owner.  At Harland and Wolff, he began with three months in the joiners’ shop, followed by a month in the cabinetmakers’ and then a further two months working on the ships. The last eighteen months of his five-year apprenticeship were spent in the drawing office. In 1901, Andrews, after working his way up through the many departments of the company, became the manager of the construction works. That same year, he also became a member of the Institution of Naval Architects. In 1907, Andrews was appointed the managing director and head of the drafting department at Harland and Wolff. During his long years of apprenticeship, study, and work, Andrews had become well liked in the company and amongst the shipyard’s employees.  On 24 June 1908, he married Helen Reilly Barbour, daughter of textile industrialist John Doherty Barbour and sister to Rt Hon Sir John Milne Barbour- known as “Milne”. Their daughter, Elizabeth Law Barber Andrews (known by her initials, “ELBA”), was born on 27 November 1910. The couple lived at Dunallan, 20 Windsor Avenue, Belfast. It is known that Andrews took Helen to view the RMS Titanic one night, shortly before Elizabeth was born. After Thomas’s death, Helen remarried; she died 22 August 1966 in Northern Ireland and is buried in the Barbour family mausoleum at Lambeg.

In 1907, Andrews began to oversee the plans for a new superliner, the RMS Olympic for the White Star Line. The Olympic and its sister ship the Titanic, which began construction in 1909, were designed by William Pirrie and general manager Alexander Carlisle along with Andrews. As he had done for the other ships he had overseen, Andrews familiarised himself with every detail of the Olympic and Titanic, in order to ensure that they were in optimal working order. Unfortunately, Andrews’s suggestions that the ship have 46 lifeboats (instead of the 20 it ended up with) as well as a double hull and water tight bulkheads that went up to B deck, were overruled.  Andrews headed a group of Harland and Wolff workers who went on the maiden voyages of the ships built by the company (the guarantee group), to observe ship operations and spot any necessary improvements. The Titanic was no exception, so Andrews and the rest of his Harland and Wolff group travelled from Belfast to Southampton on Titanic for the beginning of her maiden voyage on 10 April 1912. During the voyage, Andrews took notes on various improvements he felt were needed, primarily cosmetic changes to various facilities. However, on 14 April, Andrews remarked to a friend that Titanic was “as nearly perfect as human brains can make her.”

On 14 April at 11:40 PM, the Titanic struck an iceberg on the ship’s starboard side. Andrews had been in his stateroom, planning changes he wanted to make to the ship, and barely noticed the collision. Captain Edward J. Smith had Andrews summoned to help examine the damage. Andrews and Captain Smith discussed the damage to the ship shortly after midnight, after Andrews had toured the damaged section of the ship and received several reports of the vessel’s damage. Andrews determined that the first five of the ship’s watertight compartments were rapidly flooding. Andrews knew that if more than four of the ship’s compartments flooded, it would inevitably sink. He relayed this information to Captain Smith, stating that it was a ‘mathematical certainty’, and adding that in his opinion, the vessel had only about an hour before it completely sank. He also informed Smith of the severe shortage of lifeboats on board the ship.  As the evacuation of the Titanic began, Andrews tirelessly searched staterooms telling the passengers to put on lifebelts and go up on deck. Several survivors testify to have met or spotted Andrews several times. It is almost possible to trace his actions during the sinking. Fully aware of the short time the ship had left and of the lack of lifeboat space for all passengers and crew, he continued to urge reluctant people into the lifeboats in the hope of filling them as fully as possible. Survivors also reported seeing Andrews frantically throwing deck chairs into the ocean for passengers to use as flotation devices.

Andrews was reportedly last seen by John Stewart, a steward on the ship at approximately 2:10 A.M.(ten minutes before the Titanic fully sank into the Atlantic): Andrews was standing alone in the first–class smoking room staring at a painting, “Plymouth Harbour”, above the fireplace, arms folded over his chest, his lifejacket lying on a nearby table. The painting depicted the entrance to Plymouth Sound, which Titanic had been expected to visit on her return voyage.  Although this has become one of the most famous legends of the sinking of the Titanic, this story, which was published in a 1912 book (Thomas Andrews: Shipbuilder) and therefore perpetuated, came from John Stewart, a steward on the ship who in fact left the ship in boat n. 15 at approximately 1:40 a.m.

There were testimonies of sightings of Andrews after that moment. It appears that Andrews stayed in the smoking room for some time to gather his thoughts, then he continued assisting with the evacuation. At around 2:00 AM, Andrews was seen back on the boat deck. The crowd had begun to stir, but there were still women reluctant to leave the ship. To be heard and to draw attention to himself, Andrews waved his arms and announced to them in a loud voice.  Another reported sighting was of Andrews frantically throwing deck chairs into the ocean for passengers to use as floating devices. Andrews then headed towards the bridge perhaps searching for Captain Smith. Andrews was last seen leaving the ship at the last moment; his body was never recovered.  Finally, on 19 April 1912, his father received a telegram from his mother’s cousin, who had spoken with survivors in New York, searching for news of Andrews. The telegram was read aloud by Andrews Sr. to the staff of the home in Comber: “INTERVIEW TITANIC’S OFFICERS. ALL UNANIMOUS THAT ANDREWS HEROIC UNTO DEATH, THINKING ONLY SAFETY OTHERS. EXTEND HEARTFELT SYMPATHY TO ALL.”