The left-handed opener's 106 was the centrepiece of England's total of 318 for three at stumps.
Having missed the 1-1 drawn Test campaign in India for what the England management said at the time were "personal" and "family" reasons, Trescothick found himself the subject of unwelcome attention when he gave a television interview stating that a virus had forced him to come home.
But the Somerset star - the only player aged over 30 in a youthful England line-up - ensured attention returned to his cricket with a 14th Test hundred, his third against Sri Lanka and second at Lord's.
"I'm delighted. It was time to move on and get things rolling again, get back into the England shirt," Trescothick, now in his 70th Test, said.
"I'm playing the same way I've played all my career. I love my cricket.
"I had been pretty nervous, the nerves of expectation. But there was a bigger release last week when I made a hundred (for Somerset) against Northamptonshire."
After over four hours at the crease, Trescothick eventually fell to off-spin star Muttiah Muralitharan, who finished with two for 69.
"He's a great bowler. The wicket didn't offer too much assistance to him but he's still a real handful," said Trescothick.
The England stalwart was well-supported by Alastair Cook in a second-wicket stand of 127 with the 21-year-old Essex left-hander, who'd made a century on Test debut against India at Nagpur in March, scoring 89 in his first Test innings on home soil.
"Another 11 runs would have been nice," admitted Cook, batting down the order at three after Trescothick's return.
"It was great batting with 'Tres', he gave me a few tips as to what to expect from Murali. But you've got to work it out for yourself. He's one of a kind. I've never faced an off-spinner like him."
England will resume on Friday with Kevin Pietersen 54 not out and nightwatchman Matthew Hoggard unbeaten on two.
Cook was in sight of becoming only the eighth player in Test history to score a century on his away and home debuts and Trescothick said his emergence was a sign of England's growing strength in depth.
"To stay in the team you have to continually play well. There are people on the inside playing well and there's also pressure from the outside."
There had been doubts over whether the public euphoria built-up during the side's Ashes series win in England last year would spill over into this season. But a near-capacity crowd, for what was the earliest start to a Test in England, was an encouraging signal.
"When we play in England we get the best crowds in the world and last summer did help bring in a new generation," said Trescothick.
Meanwhile Sri Lanka coach Tom Moody reflected on a tough day for his side.
"It looks a very good wicket but not everything went our way."
Murali's 27 overs, in his first Test at Lord's, were nine more than any other Sri Lanka bowler managed but former Australia international Moody joked: "Murali's been overbowled for 10 years.
"He thrives on bowling, that's why he's the champion he is."