Yet this morning, the 41-year-old will wake up at his home in Shepherds Bush, west London, pour himself a cup of coffee and turn his back on a play that could finally have been the making of him.
Who's the Daddy?, the farce combining sexual shenanigans at the Spectator magazine with the downfall of a blind Home Secretary, ends its sell-out run tonight in Islington. It is that rare thing, a smash hit with both critics and punters, so well regarded it threatened to establish Young as a serious dramatist rather than the talented but mercurial operator many had him down for.
So the news that Who's the Daddy? will never be performed again has caused much head-scratching as well as disappointment. Spurning several offers, Young and his co-writer have decided there will be no transfer to the West End, and no revival at a later date. And the reason is deference to the feelings of Boris Johnson, his boss at the Spectator (where Young is the resident theatre critic) and a figure mercilessly lampooned in the show.
"We've decided to spare Boris's blushes," he explains. "When Lloyd Evans, my co-writer, and I first decided to write the play, everyone said 'Boris will fire you'. But he didn't. If he had done so, we'd have had no qualms about transferring. But because he's behaved so well he's shamed us into acting in kind."
Johnson is not the only one feeling relieved. Young also had a ringside seat for the affair between Johnson and the columnist Petronella Wyatt, which nearly wrecked his marriage. Then there was the affair between David Blunkett and the Spectator's publisher, Kimberly Quinn, which forced the former home secretary out of office.
If the decision is no small sacrifice for Young, it has not come as a complete surprise to his friends, who suggest that marriage and fatherhood have mellowed him. "At one time Toby was happy to piss on anyone to get on," said one. "But that's all changed."
Young is hardly short of success. Yet for a journalist who became a contributing editor for Vanity Fair at 31, it might be said that his career had not lived up to expectation.
"Some people think we'll never write such a successful play again," admits Young. "It was a unique set of circumstances. But Lloyd and I are confident we can make lightning strike twice. We are working on another farce about the Royal Family, which will certainly be irreverent. It's more Ray Cooney than Ortonesque, though."
Boris Johnson has neither seen Who's the Daddy? nor read it, which may be just as well, considering that at the end (which can now be safely revealed) Kimberly Quinn gives birth to a pair of blond mop-topped twins.
Blunkett's lawyers sent Young a shot across the bows, warning they would keep a close eye on the play. Yet of all the protagonists on stage, the former home secretary seemed the most vulnerable.
"We stepped back from portraying him as a figure of fun," Young says. "He comes across as an absurd, power-crazed sex maniac. But at the same time he is also an innocent victim who is ruthlessly taken advantage of in the cut-throat, back-stabbing world he found himself in."
Fame and fortune are not completely off the Young agenda. He hopes that pulling the play may even work to his advantage. "Lloyd and I hope that all those people who haven't seen it will have an extremely positive impression of what they've missed. Hopefully it will become a legendary comedy that only a privileged few saw. So our reputation will be higher than it would have been."