"It only took a year but @StateDept finally let me have my own @twitter account. #JKTweetsAgain," Kerry wrote in his first tweet in some 298 days on his account @JohnKerry.
A few hours later he was trumpeting an event tomorrow, when he will drop the puck at a Washington Capitals game as a way of highlighting the US ice hockey team taking part in the Winter Olympics in Sochi.
"Do love hockey. Look forward to dropping the puck at @washcaps game Thursday. #GoTeamUSA#OlympicSpirit," wrote Kerry, who is a known hockey fan and player.
On Monday he had paid tribute to US actor Philip Seymour Hoffman who died at the weekend from a suspected drugs overdose.
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"Hard to believe Philip Seymour Hoffman's gone," Kerry tweeted on @StateDept, calling him an "incredible actor (who) really became Capote."
Kerry's spokeswoman Jen Psaki said "We just determined that it was the right time, a year in, for the secretary to be able to share his own personal voice and engage with people around the world about foreign policy."