Majewski edged out Germany's world champion David Storl and Reese Hoffa of the United States who took silver and bronze respectively with a season's best throw of 21.89 metres.
He led with his third attempt inside a lively Olympic stadium and after Germany's second-placed David Storl fouled with his final throw he put the gloss on a confirmed gold with a final effort landing two centimetres further out.
The 30-year-old Pole, who is the first man to win the event twice since American Parry O'Brien in 1952 and 1956, hugged his rivals warmly before running across track to get a Polish flag.
And after the Pole had won the inaugural London gold on the field, the Ethiopian runner claimed the first on the track by storming to 10,000 metres victory.
Dibaba, 26, has hardly competed at the longest track event since winning the 5,000 and 10,000 double in Beijing but put her injury hit years behind her to take gold in 30 minutes, 20.75 seconds.
"I have never been happier like today," Dibaba said. "It is very special. I have worked hard for this."
Known as the "baby-faced destroyer", Dibaba burst clear at the bell and quickly put distance between herself and chasing Kenyan duo Sally Kipyego and Vivian Cheruiyot.
Kipyego took silver in 30:26.37 with double world champion Cheruiyot, never in a position to utilise her feared finishing kick, coming home third in 30:30.44.
Dibaba was the first to win back to back titles over the distance and has emulated her cousin Derartu Tulu (1992 and 2000) to become the second woman to win two Olympic golds in the 10,000.
Draped in an Ethiopian flag, she celebrated with a lap of the track alongside team mates Werknesh Kidane (fourth) and Beleynesh Oljira (fifth).
Silver and bronze were Kenya's first medals since the 10,000 was introduced for women at the 1988 Games in Seoul.
Olympic champion Irving Saladino's bid to defend his long jump title at the London Games came to a premature end when the Panamanian failed to record a legal jump in qualifying
The 29-year-old, Panama's first Olympic champion and also a world champion in 2007, carried his country's flag at the opening ceremony but fouled all three attempts.
"I had trouble with the wind," he told reporters. "Sometimes it was blowing from the front. Sometimes from the back. But I am not disappointed. I am sure I will be back."
Saladino, who said he had not started training until April after knee surgery, joined 2004 Olympic champion Dwight Phillips in missing Saturday's final.
Phillips, four times a world champion, had surgery on an Achilles injury and missed the US trials, leaving an already open long jump competition even more difficult to call.
Russian Sergey Morgunov, who had the second best jump of the year coming into London, also missed out on the final 12, managing a jump of just 7.92 metres.
World indoor champion Mauro Vinicius da Silva of Brazil and American Marquise Goodwin led the qualifying session with jumps of 8.11 metres and Russian Alexandr Menkov was third (8.09) on an evening when only seven competitors managed over eight metres.
British hopefuls Greg Rutherford (8.08), the world leader, and Christopher Tomlinson (8.06) qualified comfortably with the fourth and fifth longest jumps.
Australia's Mitch Watt, who owns four of the five best jumps of the last two years, was ninth with a jump of 7.97 and will be joined in the final by compatriot Henry Frayne (7.95), who also competes in the triple jump.
- David Storl