He was the son and heir of John Reynell (d.1363/4) of Trumpington in Cambridgeshire (stated in the Heraldic Visitation of Devon of 1620 to have been a Member of Parliament for Cambridgeshire in 1351/2) by his wife Maud de Fulburne (alias Fulborne, etc.), daughter of Giles de Fulburne of Cambridgeshire. His identity is confused in the pedigree in the Heraldic Visitation of Devon of 1620, which shows his son Walter, rather than himself, as the husband of Margaret Stighull. His uncle was SirHugh Reynell (fl.1275) (alias Hugues de Revel), the 19th (or 20th) Grand Master of the Knights of St John of Jerusalem in 1275, who is memorialised by a small harbour in Malta called Renelle. The earliest recorded member of the Reynell family is Sir Richard Reynell (d.pre-1213) (alias Reinell, Reynolds, etc.), of Pitney in Somerset, Sheriff of Devon in 1191–4, Walter Reynell’s great-great-great grandfather.
He married three times:
- Firstly, at some time before 1376, he married a certain Agnes;
- Secondly, before 1383, he married Margaret Stighull, daughter and heiress of William Stighull (alias Styl, Stigill, etc.) by his wife Elizabeth Malston, daughter and heiress of Robert Malston of Malston, in the parish of Sherford in Devon, by whom he had children including:
- Walter Reynell (died 1478) of Malston, eldest son and heir, a Member of Parliament for Devon in 1454/5, who married Joane Walrond, a daughter of William Walrond of Bradfield in the parish of Uffculme, Devon.
- John Reynell (fl.1427/8), a Member of Parliament for Devon in 1427/8, who married Agnes Chichester, a daughter of the Chichester family then recently seated at Raleigh in the parish of Pilton, Devon. He predeceased his father without children.
- Robert Reynell, died childless;
- Elinor Reynell (d. 9 April 1507), wife of William Fowell (died 23 March 1507) of Fowelscombe in the parish of Ugborough, Devon, a Member of Parliament for Totnes in Devon in 1455. The couple’s monument survives in Ugborough Church.
- Alice Reynell, who married a member of the Trevelyan family.
- Thirdly, at some time before 1400, he married Joan Bassingbourne, daughter and heiress of John Bassingbourne of Badlingham, and cousin and heiress of Alan le Francis, by whom he had 3 sons and 4 daughters.