Pairing up with Canadian teenager Victoria Mboko the 44-year-old served powerfully and delivered some stunning returns as the duo beat third seeds Nicole Melichar-Martinez and Erin Routliffe 7-6 (7-2) 6-2.
In front of her daughters Olympia and Adira the 23-time grand slam singles champion received a rapturous reception in early evening sun by a home crowd already cheered by English successes.
Williams last played professionally at the US Open in September 2022, going out to Ajla Tomljanovic in the third round in New York in front of more than 20,000 people - a night the Australian has said she'll always remember.
The long break hardly seemed to have affected her as Williams secured two of the pair's points en route to a first-game victory, then immediately broke serve in the next before reaching a 182 kph in her first service game.
Williams subsequently dropped her second service game to level the first set up, despite cranking it up to 191kph but the north American pair easily won the tie-break.
They cruised through the second set. Singles, with so much more ground to cover, would be a different proposition but in doubles the Williams-Mboko pairing looks formidable.
"It was so much fun, it felt so natural playing with Vicky," a beaming Williams said on court. "I guess I've got nothing better to do, I'm tired of sitting at home, my kids are out of school this summer so why not?"
Asked if she will compete at Wimbledon Williams said she still had not decided.
Earlier the only Australian woman in the main draw went out, Maddison Inglis going down in three sets to seventh-seeded Sorana Cirstea 6-4 5-7 6-2.
The 151-world ranked Inglis had scrapped her way through qualifying, scoring a victory over world No.81 Alycia Parks on the way, but found the Romanian too strong despite a second set fightback.
Cirstea, the world No.18, was coming off reaching the French Open last eight where she lost to eventual winner Mirra Andreeva.
Inglis pushed her hard, battling for two hours 26 minutes on a windy day in London.
Britain's Katie Boulter, Alex de Minaur's fiancee, produced the surprise of the day defeating Canadian eighth-seed Layla Fernandez 3-6 7-6 (7-4) 7-5.
With Emma Raducanu beating Anna Blinkova 6-0 6-3 it made a day of double delight for the home audience.
Defending champion Tatjana Maria, who complained about having to come through qualifying rather than being given a wildcard, progressed with a 6-3 6-3 victory over Maria Sakkari.
