Berwick had children by both his marriages.
His descendants were the French Ducs de Fitz-James and the Spanish Duques de Liria and later the Dukes of Alba.

Berwick fell in love with General Patrick Sarsfield's 19-year-old pregnant widow.
They married in Saint-Germain-en-Laye (Yvelines) on 26 March 1695, two years after Sarsfield's death in the Battle of Landen on 29 July 1693.
This was Honora, Countess of Lucan (formerly known as Lady Honora Burke or Lady Honora de Burgh; b. Portumna Castle, Co. Galway, 1674 – d. Pézenas, 16 January 1698), the daughter of John Burke, 9th Earl of Clanricarde, an Anglo-Irish peer.
Berwick raised Sarsfield's son, James Sarsfield, 2nd Earl of Lucan, who died childless in 1718, as his own.
Berwick and the Countess had a son:
James Francis Fitz-James Stuart, who inherited the title Duke of Berwick on his father's death, or Jacobo Francisco Fitz-James Stuart, 2nd Duke of Berwick, 2nd Duke of Liria and Xerica (Saint-Germain-en-Laye, Yvelines, 21 October 1696 – Naples, Italy, 2 June 1738).
 He married Catalina Ventura Colón de Portugal, Duchess of Veragua and Duchess of La Vega, a descendant of Christopher Columbus.

After Honora Burke's death just three years later in 1698, Berwick married Anne Bulkeley (d. 12 June 1751), daughter of Henry Bulkeley (Master of the Household to James II),  in Paris on 18 April 1700.
They had eight sons and five daughters:
Berwick had children by both his marriages. His descendants were the French Ducs de Fitz-James and the Spanish Duques de Liria and later the Dukes of Alba.
Berwick fell in love with General Patrick Sarsfield's 19-year-old pregnant widow. They married in Saint-Germain-en-Laye (Yvelines) on 26 March 1695, two years after Sarsfield's death in the Battle of Landen on 29 July 1693. This was Honora, Countess of Lucan (formerly known as Lady Honora Burke or Lady Honora de Burgh; b. Portumna Castle, Co. Galway, 1674 – d. Pézenas, 16 January 1698), the daughter of John Burke, 9th Earl of Clanricarde, an Anglo-Irish peer. Berwick raised Sarsfield's son, James Sarsfield, 2nd Earl of Lucan, who died childless in 1718, as his own. Berwick and the Countess had a son:
James Francis Fitz-James Stuart, who inherited the title Duke of Berwick on his father's death, or Jacobo Francisco Fitz-James Stuart, 2nd Duke of Berwick, 2nd Duke of Liria and Xerica (Saint-Germain-en-Laye, Yvelines, 21 October 1696 – Naples, Italy, 2 June 1738).  He married Catalina Ventura Colón de Portugal, Duchess of Veragua and Duchess of La Vega, a descendant of Christopher Columbus.
After Honora Burke's death just three years later in 1698, Berwick married Anne Bulkeley (d. 12 June 1751), daughter of Henry Bulkeley (Master of the Household to James II),  in Paris on 18 April 1700. They had eight sons and five daughters:
James FitzJames, 1st Duke of Berwick