Ryecart was born in Warwickshire. His first West End appearance was in Bernard Shaw's Candida at the Albery Theatre, playing the young poet Marchbanks opposite Deborah Kerr, directed by Michael Blakemore. Among a string of fine reviews Bernard Levin in the Sunday Times described his performance as "supernova" and that he had not seen "such a talent in embryo since the young Richard Burton". Ryecart has continued working in theatre, television and film (his last film role Lord Wigram in "The King's Speech") with lead roles in the classics of Shaw, Sheridan, and Shakespeare to light comedies, TV situation comedy, thrillers and musicals. Among his notable credits in London are Jack Absolute in "The Rivals" with Michael Hordern as his father and Geraldine McKewan as Mrs Malaprop, and Lord Goring in Peter Hall's "An Ideal Husband". He has acted on many British television shows since the mid-seventies including Lillie, Romeo and Juliet, The Professionals, Minder, Rumpole of the Bailey, Lovejoy, Coming Home and Holby City. In 1986 he appeared in the Doctor Who serial The Trial of a Time Lord in the Mindwarp segment. He was one of the lead characters in the BBC TV comedy series The High Life playing Captain Hilary Duff. He played Hugo Latimer in the BBC series Trainer. He also appeared in the 1997 Agatha Christie's Poirot episode, Dumb Witness., and for the BBC in My Son My Son. Also Dalziel & Pascoe episode and many mini series for the U.S. He played Sir Hugh Bodrugan in the 2015 BBC series of Poldark. In 2016, he played the role of the Duke of Norfolk in the Netflix series The Crown.
His extensive theatre credits include The Beastly Beatitudes of Balthazar B by J P Donleavy in London's West End which he also produced, first playing Balthazar to Simon Callow's playing Beefy, (who was later replaced by Billy Connolly). Numerous tours include "Donkeys Years", "Rebecca", "Tunes of Glory" and "The Millionairess" opposite Raquel Welch. He also produced, at the Garrick Theatre London (and later redirected for tour and the Edinburgh Festival 2011) "Jus' like That!" the highly successful affectionate tribute to the great Tommy Cooper, written by John Fisher.
His film credits include A Bridge Too Far (1977), Silver Dream Racer (1980), Arthur the King (1985), Prisoner of Honor (1991), Parting Shots (1999) and The King's Speech (2010).
He was married to English actress Marsha Fitzalan from 4 July 1977 until their divorce in 1995. She was the third daughter of the late 17th Duke of Norfolk and they met at drama school The Webber Douglas Academy. They have three grown up children: Mariella Celia (born 1982), Jemima Carrie (1984), (both married) and Frederick William Hamlet (1987). Ryecart lives in London.