The main structure is in Portland stone.
It takes the form of a vaulted colonnade or pavilion reminiscent of a Doric temple but open at both ends.
After the Arch of Remembrance in Leicester, it is Lutyens' second-largest war memorial in the United Kingdom, and is the only British First World War memorial dedicated exclusively to merchant seamen.
It is raised on a platform slightly above street level, oriented east to west and accessed from the street by a set of five stone steps at each end.
The structure is 21.5 metres (71 feet) long by 7 metres (23 ft) wide and up to 10 metres (33 ft) tall.
It consists of three bays on either side, created by eight alternating square piers and six pairs of round columns.
The eight piers are clad in rectangular bronze panels to give the impression of rustication.
The panels (divided into 24 numbered sections) contain the names of missing mariners, ordered by ship name and then alphabetically following the name of the captain or master.
The vessels of the Merchant Navy and Fishing Fleets are listed separately.
Above the bays is a Doric entablature.
The low, pitched roof has shallow parapets on either side and gabled ends; on top, in the centre, is a large square attic which supports a large stone drum.
The attic is similar to Lutyens' original design for the York City War Memorial, which featured a Stone of Remembrance rather than a drum.
The sculptural element is the work of William Reid Dick, who worked on several other war memorials, including the Menin Gate in Ypres, Belgium.
  
The memorial's main dedication is in bronze letters to the front (south) of the attic: TO THE GLORY OF GOD AND TO THE HONOUR OF TWELVE THOUSAND OF THE MERCHANT NAVY AND FISHING FLEETS WHO HAVE NO GRAVE BUT THE SEA; above it are the dates of the First World War (1914–1918), which are also carved into the stone on north side.
To either side are decorative bronze wreaths.
On the inside, the floor is in black and white stone in a chequerboard pattern.
On the north side, bronze spikes occupy the otherwise-open bays.

The largest single loss of life commemorated on the memorial is from the sinking of the RMS Lusitania on 7 May 1915.
Of the 1,200 dead, over 350 British crew members are commemorated on the Mercantile Marine memorial.
In total, the First World War memorial records the names of some 12,000 casualties.

In his biography of Lutyens, Michael Barker described the design as "dignified classicism"; another Lutyens biographer, Christopher Hussey, described it as a "classical shrine".
Tim Skelton, author of Lutyens and the Great War, notes the similarity of the colonnade to the shelter buildings in Lutyens' cemeteries in France and Belgium and suggests that the memorial would be "equally well at home on the Western Front as in the heart of London".
The resemblance to the cemetery buildings is also noted by the Dutch architect Jeroen Geurst, who compares it in particular to those at Hooge Crater in Belgium and Serre Road in France.
In the opinion of the historian David Crane, the memorial never recovered from its "miserable start" and is consequently the least well-known of the IWGC's major works following the First World War.
The main structure is in Portland stone. It takes the form of a vaulted colonnade or pavilion reminiscent of a Doric temple but open at both ends. After the Arch of Remembrance in Leicester, it is Lutyens' second-largest war memorial in the United Kingdom, and is the only British First World War memorial dedicated exclusively to merchant seamen. It is raised on a platform slightly above street level, oriented east to west and accessed from the street by a set of five stone steps at each end. The structure is 21.5 metres (71 feet) long by 7 metres (23 ft) wide and up to 10 metres (33 ft) tall. It consists of three bays on either side, created by eight alternating square piers and six pairs of round columns. The eight piers are clad in rectangular bronze panels to give the impression of rustication. The panels (divided into 24 numbered sections) contain the names of missing mariners, ordered by ship name and then alphabetically following the name of the captain or master. The vessels of the Merchant Navy and Fishing Fleets are listed separately. Above the bays is a Doric entablature. The low, pitched roof has shallow parapets on either side and gabled ends; on top, in the centre, is a large square attic which supports a large stone drum. The attic is similar to Lutyens' original design for the York City War Memorial, which featured a Stone of Remembrance rather than a drum. The sculptural element is the work of William Reid Dick, who worked on several other war memorials, including the Menin Gate in Ypres, Belgium.   
The memorial's main dedication is in bronze letters to the front (south) of the attic: TO THE GLORY OF GOD AND TO THE HONOUR OF TWELVE THOUSAND OF THE MERCHANT NAVY AND FISHING FLEETS WHO HAVE NO GRAVE BUT THE SEA; above it are the dates of the First World War (1914–1918), which are also carved into the stone on north side. To either side are decorative bronze wreaths. On the inside, the floor is in black and white stone in a chequerboard pattern. On the north side, bronze spikes occupy the otherwise-open bays.
The largest single loss of life commemorated on the memorial is from the sinking of the RMS Lusitania on 7 May 1915. Of the 1,200 dead, over 350 British crew members are commemorated on the Mercantile Marine memorial. In total, the First World War memorial records the names of some 12,000 casualties.
In his biography of Lutyens, Michael Barker described the design as "dignified classicism"; another Lutyens biographer, Christopher Hussey, described it as a "classical shrine". Tim Skelton, author of Lutyens and the Great War, notes the similarity of the colonnade to the shelter buildings in Lutyens' cemeteries in France and Belgium and suggests that the memorial would be "equally well at home on the Western Front as in the heart of London". The resemblance to the cemetery buildings is also noted by the Dutch architect Jeroen Geurst, who compares it in particular to those at Hooge Crater in Belgium and Serre Road in France. In the opinion of the historian David Crane, the memorial never recovered from its "miserable start" and is consequently the least well-known of the IWGC's major works following the First World War.
Tower Hill Memorial