- Apr 1 Royal Canadian Mint formally forms as a Crown Corporation
- Apr 1 Seattle Pilots trade little-known minor league outfielder Lou Piniella to KC Royals for 2 prospects; hits .282 with 11 HRs & 68 RBI to win AL Rookie of the Year; becomes leading MLB manager
- Apr 1 The Hawker Siddeley Harrier (vertical take-off fighter) enters service with the RAF.
- Apr 2 Toronto center Forbes Kennedy sets a Stanley Cup playoff record for most penalties in one game with 8 as the Maple Leafs crash 10-0 to the Bruins at Boston; Boston’s first NHL playoff victory in 10 years
- Apr 3 Vietnam War: U.S. Secretary of Defense Melvin Laird announces that the United States will start a policy of "Vietnamization", reducing American involvement
- Apr 4 Haskell Karp receives the 1st temporary artificial heart, implanted by surgeon Denton Cooley at Texas Heart Institute in Houston
- Apr 5 Massive anti-Vietnam War demonstrations occur in many U.S. cities
- Apr 7 Dodgers' Bill Singer is credited with 1st official save, against Reds
- Apr 7 Supreme Court strikes down laws prohibiting private possession of obscene material
Event of Interest
Apr 7 Ted Williams begins managing Washington Senators, they lose to Yanks 8-4

Ted Williams
- Apr 7 The Internet's symbolic birth date: publication of RFC 1
- Apr 8 First Major League Baseball game featuring a Canadian team; Montréal Expos beats NY Mets, 11-10 at Shea Stadium; KC Royals, SD Padres and Seattle Pilots also win on debut
- Apr 8 Expansion teams Royals, Expos, Padres & Pilots win their 1st games
- Apr 9 1st flight of Concorde 002 (Filton-Bristol)
- Apr 9 Chic Cub Billy Williams hits 4 consecutive doubles beat Phillies 11-3
- Apr 12 Simon & Garfunkel releases "Boxer"
- Apr 12 Wales beats England, 30-9 at the National Stadium, Cardiff to clinch their 16th Five Nations Rugby Championship and 11th Triple Crown
- Apr 13 33rd US Masters Tournament, Augusta National GC: George Archer wins his only major title, 1 stroke ahead of runners-up Billy Casper, George Knudson, and Tom Weiskopf
- Apr 13 Closure of the Brisbane tramway network.
- Apr 14 First regular-season MLB game played outside the United States; Montreal Expos beat St. Louis Cardinals, 8-7 at Parc Jarry, Montreal
Academy Awards
Apr 14 41st Academy Awards: "Oliver", Cliff Robertson & Katharine Hepburn and Barbra Streisand win (1st ever tie for best actress)
Event of Interest
Apr 17 Alexander Dubček forced to resign as first secretary of Czechoslovakia's Communist Party

Alexander Dubček
- Apr 17 Mont Expos Bill Stoneman no-hits Phillies, 7-0
Event of Interest
Apr 17 Sirhan Sirhan is convicted of assassinating US Senator Robert F. Kennedy

Robert F. Kennedy
- Apr 17 The Band (formerly The Hawks), perform their 1st concert
- Apr 17 People's Democracy activist Bernadette Devlin becomes the youngest woman Member of Parliament ever elected to Westminster at 21 years old
- Apr 18 Greek actress and activist Melina Mercouri establishes Greek Aid Fund
- Apr 19 Serious rioting in the Bogside area of Derry following clashes between Northern Ireland Civil Rights Association marchers and Loyalists and members of the Royal Ulster Constabulary
- Apr 20 23rd Tony Awards: Great White Hope & 1776 win
- Apr 20 Bombs planted by Loyalists members of the Ulster Volunteer Force and the Ulster Protestant Volunteers explode at Silent Valley reservoir in County Down and at an electricity pylon at Kilmore, County Armagh
- Apr 21 73rd Boston Marathon: Yoshiaki Unetani of Japan wins in 2:13:49; American Sara Mae Berman 1st woman in 3:22:46 (unsanctioned)
- Apr 21 The Ministry of Defence in London announces that British troops would be used in Northern Ireland to guard key public installations following a series of bombings
- Apr 22 1st human eye transplant performed
Boxing Title Fight
Apr 22 Joe Frazier KOs Dave Zyglewick in 1 for heavyweight boxing title

Joe Frazier
Event of Interest
Apr 23 LA Laker Jerry West scores 53 points

Jerry West
- Apr 23 Over 1000 square miles flooded in Shantung Province, China
- Apr 23 Sirhan Sirhan sentenced to death for killing US Senator Robert F. Kennedy (later computed to life sentence)
- Apr 23 The Unionist Parliamentary Party votes by 28 to 22 to introduce universal adult suffrage in local government elections in Northern Ireland; the demand for 'one man, one vote' had been one of the most powerful slogans of the civil rights movement
- Apr 24 Marshall Lin Biao named Mao's designated successor as the sole Vice Chairman of the Communist Party of China
- Apr 24 Lebanese army in battle with Palestinians
Event of Interest
Apr 24 Paul McCartney says there is no truth to rumors he is dead

Paul McCartney
- Apr 24 US B-52's drop 3,000 ton bombs at Cambodian boundary
- Apr 24 Car firm British Leyland launch the Austin Maxi in Oporto Portugal
- Apr 24 Loyalist members of the Ulster Volunteer Force (UVF) and the Ulster Protestant Volunteers (UPV) explode a bomb at a water pipeline between Lough Neagh and Belfast, Northern Ireland
- Apr 25 5,400th & last episode of BBC Radio serial "The Dales" (formerly "Mrs Dale's Diary")
- Apr 26 "Celebration" closes at Ambassador Theater NYC after 110 performances
- Apr 26 "George M!" closes at Palace Theater NYC after 435 performances
- Apr 26 Firestone World Bowling Tournament (Mercury Open) won by Jim Godman
Event of Interest
Apr 28 Charles de Gaulle resigns as president of France

Charles de Gaulle
- Apr 28 King Crismson with Greg Lake & Ian McDonald debuts
Event of Interest
Apr 28 Northern Ireland Prime Minister Terence O'Neill resigns and is replaced later by James Chichester-Clark.

Terence O'Neill

James Chichester-Clark
Music Awards
Apr 28 4th Academy of Country Music Awards: Glen Campbell and Cathie Taylor win

Glen Campbell