Howard was born in Cliftonville, Kent, England, the son of Mabel Grey (Wallace) and Arthur John Howard. He was educated at Clifton College (to which he left in his will a substantial legacy for a drama scholarship) and at the Royal Academy of Dramatic Art (RADA), acting on the London stage for several years before World War II. His first paid work was in the play Revolt in a Reformatory (1934), before he left RADA in 1935 to take small roles. Although stories of his courageous wartime service in the British Army's Royal Corps of Signals earned him much respect among fellow actors and fans alike, files held in the Public Record Office reveal that he had actually been discharged from the British Army in 1943 for mental instability and having a "psychopathic personality". The story, which surfaced in Terence Pettigrew's biography of the actor, published by Peter Owen in 2001, was initially denied by Howard's widow, actress Helen Cherry. Later, confronted with official records, she told the Daily Telegraph (24 June 2001) that his mother had claimed he was a holder of the Military Cross. She added that Howard had an honourable military record and "had nothing to be ashamed of".
| Movie | German Concentration Camps Factual Survey | Narrator (fragment version) | 2017-01-06 |
| Movie | The Unholy | Father Silva | 1988-04-22 |
| Movie | The Dawning | Grandfather | 1988-06-08 |
| Movie | Hand in Glove | Vicar | 1987-01-01 |
| Movie | White Mischief | Jack Soames | 1987-11-10 |
| Movie | Time After Time | Brigadier Croshawe | 1986-01-26 |
| Series | Peter the Great | Sir Isaac Newton | 1986-02-02 |
| Series | Shaka Zulu | Lord Charles Somerset | 1986-10-24 |
| Movie | Christmas Eve | Maitland | 1986-12-22 |
| Movie | Foreign Body | Dr Stirry | 1986-09-26 |
| Movie | Dust | Father | 1985-09-11 |
| Movie | Sword of the Valiant: The Legend of Sir Gawain and the Green Knight | The King | 1984-08-17 |
| Series | George Washington | Lord Fairfax | 1984-04-08 |
| Movie | The Making of 'Superman: The Movie' | Self | 1982-01-24 |
| Movie | The Deadly Game | Gustave Kummer | 1982-07-22 |
| Movie | Gandhi | Judge Broomfield | 1982-12-01 |
| Movie | The Missionary | Lord Henry Ames | 1982-11-02 |
| Movie | Light Years Away | Yoshka Poliakeff | 1981-05-20 |
| Series | Shillingbury Tales | Dan 'Saltie' Wicklow | 1980-01-06 |
| Movie | The Sea Wolves | Jack Cartwright | 1980-07-03 |
| Movie | Flashpoint Africa | Program Controller | 1980-01-01 |
| Movie | The Shillingbury Blowers | Saltie | 1980-01-06 |
| Movie | Sir Henry at Rawlinson End | Sir Henry Rawlinson | 1980-11-07 |
| Movie | Staying On | Col. Tusker Smalley | 1980-12-28 |
| Movie | Windwalker | Windwalker | 1980-12-12 |
| Movie | Superman II | Krypton Elder (archive footage) (uncredited) | 1980-12-12 |
| Movie | Hurricane | Father Malone | 1979-04-12 |
| Movie | The Spirit of Adventure: Night Flight | Riviere | 1979-01-26 |
| Movie | Meteor | Sir Michael Hughes | 1979-10-19 |
| Movie | Stevie | The Man | 1978-09-15 |
| Movie | Slavers | Alec Mackenzie | 1978-02-24 |
| Movie | Superman | 1st Elder | 1978-12-14 |
| Movie | The Last Remake of Beau Geste | Sir Hector | 1977-06-15 |
| Movie | Aces High | Lieutenant Colonel Silkin | 1976-05-19 |
| Movie | Death in the Sun | Johannes | 1976-03-15 |
| Movie | The Bawdy Adventures of Tom Jones | Squire Western | 1976-08-01 |
| Series | Origins of the Mafia | Don Consalvo Saccone | 1976-11-19 |
| Movie | The Adventures of Eliza Fraser | Capt. Foster Fyans | 1976-12-16 |
| Movie | Conduct Unbecoming | Colonnello Benjamin Strang | 1975-10-04 |
| Movie | The Count of Monte-Cristo | Abbé Faria | 1975-10-31 |
| Movie | Hennessy | Comdr. Rice | 1975-12-31 |
| Movie | Who? | Colonel Azarin | 1974-04-18 |
| Movie | Craze | Supt. Bellamy | 1974-05-16 |
| Movie | 11 Harrowhouse | Clyde Massey | 1974-09-26 |
| Movie | Persecution | Paul Bellamy | 1974-11-07 |
| Movie | The Offence | Lieutenant Cartwright, Detective Superintendant | 1973-01-11 |
| Movie | Ludwig | Richard Wagner | 1973-03-07 |
| Movie | A Doll's House | Dr. Rank | 1973-08-16 |
| Movie | The Catholics | The Abbot | 1973-11-29 |
| Movie | Pope Joan | Pope Leo | 1972-08-16 |
| Movie | Mary, Queen of Scots | William Cecil | 1971-12-22 |
| Movie | The Night Visitor | Inspector | 1971-02-10 |
| Movie | Catch Me a Spy | Trevor Dawson | 1971-09-06 |
| Movie | Kidnapped | Lord Advocate | 1971-12-22 |
| Movie | Twinky | Twinky's Grandfather | 1970-01-06 |
| Movie | Ryan's Daughter | Father Collins | 1970-03-19 |
| Movie | Battle of Britain | Air Vice Marshal Keith Park | 1969-09-15 |
| Movie | The Charge of the Light Brigade | Lord Cardigan | 1968-04-10 |
| Movie | The Long Duel | Freddie Young | 1967-07-27 |
| Movie | Pretty Polly | Robert Hook | 1967-10-19 |
| Movie | The Poppy Is Also a Flower | Sam Lincoln | 1966-05-20 |
| Movie | Triple Cross | Freddie Young (Distinguished Civilian) | 1966-12-09 |
| Movie | Operation Crossbow | Professor Lindemann | 1965-04-01 |
| Movie | Von Ryan's Express | Major Eric Fincham | 1965-06-23 |
| Movie | Morituri | Colonel Statter | 1965-08-24 |
| Movie | The Liquidator | Mostyn | 1965-11-01 |
| Movie | Man in the Middle | Major Kensington | 1964-01-27 |
| Movie | Father Goose | Commander Frank Houghton | 1964-12-10 |
| Movie | The Invincible Mr. Disraeli | Benjamin Disraeli | 1963-04-03 |
| Movie | The Lion | John Bullit | 1962-08-19 |
| Movie | Mutiny on the Bounty | Capt. William Bligh | 1962-11-08 |
| Movie | Hedda Gabler | Ejlert Lövborg | 1962-12-28 |
| Movie | The Hiding Place | Robert Wilson | 1960-03-22 |
| Movie | Moment of Danger | John Bain | 1960-01-26 |
| Movie | Sons and Lovers | Walter Morel | 1960-06-23 |
| Movie | The Key | Capt. Chris Ford | 1958-05-28 |
| Movie | The Roots of Heaven | Morel | 1958-10-15 |
| Movie | Interpol | Frank McNally | 1957-04-02 |
| Movie | Manuela | James Prothero | 1957-07-18 |
| Movie | Run for the Sun | Browne | 1956-07-30 |
| Movie | Around the World in 80 Days | Denis Fallentin | 1956-10-17 |
| Movie | Lovers' Net | Inspector Lewis | 1955-01-18 |
| Movie | The Cockleshell Heroes | Captain Thompson | 1955-11-16 |
| Movie | The Stranger's Hand | Major Roger Court | 1954-01-20 |
| Movie | The Heart of the Matter | Harry Scobie | 1953-11-03 |
| Movie | Gift Horse | Lt. Cmdr Hugh Alginon Fraser | 1952-06-01 |
| Movie | Lady Godiva Rides Again | Guest at Theater Accepting Program (uncredited) | 1951-10-25 |
| Movie | Outcast of the Islands | Peter Willems | 1951-11-15 |
| Movie | The Clouded Yellow | Maj. David Somers | 1950-11-21 |
| Movie | Golden Salamander | David Redfern | 1950-02-01 |
| Movie | Odette | Captain Peter Churchill | 1950-10-02 |
| Movie | The Passionate Friends | Prof. Steven Stratton | 1949-01-26 |
| Movie | The Third Man | Major Calloway | 1949-08-31 |
| Movie | They Made Me a Fugitive | George Clement 'Clem' Morgan | 1947-06-24 |
| Movie | So Well Remembered | Dr. Richard Whiteside | 1947-07-09 |
| Movie | Green for Danger | Dr. Barnes | 1946-12-07 |
| Movie | I See a Dark Stranger | Lt. David Bayne | 1946-07-04 |
| Movie | The Way to the Stars | Squadron Leader Carter | 1945-06-16 |
| Movie | Brief Encounter | Dr. Alec Harvey | 1945-11-24 |
| Movie | The Way Ahead | Officer on Ship (uncredited) | 1944-06-09 |