On 11 November 1985, Sassoon was among sixteen Great War poets commemorated on a slate stone unveiled in Westminster Abbey's Poet's Corner. The inscription on the stone was written by friend and fellow War poet Wilfred Owen. It reads: "My subject is War, and the pity of War. The Poetry is in the pity."
The year 2003 saw the publication of Memorial Tablet, an authorised audio CD of readings by Sassoon recorded during the late 1950s. These included extracts from Memoirs of an Infantry Officer and The Weald of Youth, as well as several war poems including Attack, The Dug-Out, At Carnoy and Died of Wounds, and postwar works. The CD also included comment on Sassoon by three of his Great War contemporaries: Edmund Blunden, Edgell Rickword and Henry Williamson.
Siegfried Sassoon's only child, George Sassoon, died of cancer in 2006. George had three children, two of whom were killed in a car crash in 1996. His daughter by his first marriage, Kendall Sassoon, is Patron-in-Chief of the Siegfried Sassoon Fellowship, and a Lady Associate Royal Welch Fusilier.
Sassoon's long-lost Military Cross turned up in a relative's attic in May 2007. Subsequently, the medal was put up for sale by his family. It was bought by the Royal Welch Fusiliers for display at their museum in Caernarfon.
Sassoon's other service medals went unclaimed until 1985 when his son George obtained them from the Army Medal Office, then based at Droitwich. The "late claim" medals consisting of the 1914-15 Star, Victory Medal and British War Medal along with Sassoon's CBE and Warrant of Appointment were auctioned by Sotheby's in 2008.
In June 2009, the University of Cambridge announced plans to purchase a valuable archive of Sassoon's papers from his family, to be added to the university library's existing Sassoon collection. On 4 November 2009 it was reported that this purchase would be supported by £550,000 from the National Heritage Memorial Fund, meaning that the University still needed to raise a further £110,000 on top of the money already received in order to meet the full £1.25 million asking price. The funds were successfully raised, and in December 2009 it was announced that the University had received the papers. Included in the collection are war diaries kept by Sassoon while he served on the Western Front and in Palestine, a draft of "A Soldier’s Declaration" (1917), notebooks from his schooldays, and post-war journals. Other items in the collection include love letters to his wife Hester, and photographs and letters from other writers. Sassoon was an undergraduate at the university, as well as being made an honorary fellow of Clare College, and the collection will be housed at the Cambridge University Library. As well as private individuals, funding came from the Monument Trust, the JP Getty Jr Trust, and Sir Siegmund Warburg's Voluntary Settlement.
In 2010, Dream Voices: Siegfried Sassoon, Memory and War, a major exhibition of Sassoon's life and archive, was held at Cambridge University.
Several of Sassoon's poems have been set to music, some during his lifetime, notably by Cyril Rootham, who co-operated with the author.
The discovery in 2013 of an early draft of one of Sassoon's best-known anti-war poems had biographers saying they would rewrite portions of their work about the poet. In the poem, 'Atrocities,' which concerned the killing of German prisoners by their British counterparts, the early draft shows that some lines were cut and others watered down. The poet's publisher was nervous about publishing the poem, and held it for publication in an expurgated version at a later date. Said Sassoon biographer Jean Moorcroft Wilson on learning of the discovery of the early draft: "This is very exciting material. I want to rewrite my biography and I probably shall be able to get some of it in. It's a treasure trove."