It started in Phoenix and continues in Boston. He still comes off the bench, but has led the Celtics to a hot finish and a playoff berth, where he became one of only a handful of players in NBA history to post a 22 point, 10 assist, 5 rebound stat line in his first ever playoff game.
Thomas was excited to get exactly where he wanted to go this season - the playoffs - despite getting there in a roundabout fashion.
"It's the next step in my career," he said last week. "I think that's where all the great players make their name — the playoffs. I'm excited about it. Just being a part of this team, and being able to turn this season around and be a factor. People really know who we are. We're ready for that stage."
On Monday Thomas was announced as the runner-up to Louis Williams as Sixth Man of the Year.
Thomas put up 15.7 points and 3.7 assists for the Suns in just under 26 minutes per game (46 games), then exploded for 19 points and 5.4 assists per game for Boston in the same 26 minutes (21 games). He barely topped that last year in Sacramento (20 and 6) despite playing nearly 10 more minutes per game.
In short, Isaiah has been en fuego for the Celtics. Overall, he led the league's bench players with 16.3 points per game.
"(The voting is) not in my control," Thomas said Monday, via ESPN. "Congrats to Lou Will. I can't say too much about it. All I'm going to say is numbers don't lie. But congrats to him, he deserves it."
But when it comes down to it, Thomas wants to be a starter. He never wanted to be up for the Sixth Man award in the first place.
Thomas has always wanted to be a starter in the league, and feels like he's earned it with his performance throughout his career. Each year before this one, he's beaten out his competition for a starting role by midseason.
This year was quite different though, and quite frustrating for Thomas as a result. Even now, taking Boston to the playoffs, he's not satisfied.
"Nobody's sold me on no sixth man role," Thomas said before Tuesday's 95-93 win over the Toronto Raptors. "I've only had a few talks with (president of basketball operations) Danny (Ainge), a few talks with (coach) Brad. This is the role for the team right now, and I'm going to take full advantage of it."
Last summer, he felt shunned by the Sacramento Kings after working his way into their starting lineup, and was disappointed in the free agent offers from teams who could have offered him a starting shot this season. But he was sold on the Suns right away, and committed to the team within hours of the official opening of the new league year. While he wouldn't get a starting spot right away, he would get the biggest contract of his career and a chance to play big minutes.
"It is important to me," Thomas, at his introductory press conference this summer, said of being a starter. "But when it comes down to winning I'll do whatever it takes to win. I want to be on a winning team. I'm all for it. At the end of the day we're going to play with each other no matter who starts and who comes off the bench it's about winning."
"Who knows?" he replied to a question of him, Dragic and Bledsoe playing together.
The Suns started the season fairly well, winning 12 of their first 20 games, including thrilling wins over San Antonio and Golden State. But even then it was obvious Thomas was not happy in his role. In an interview with Sam Amick of USA Today in mid November, Thomas said he was itching to start.
"I'd be lying to you if I said it doesn't bother me that I don't start," Thomas said to Amick. "But I'm going to do what's best for this team and continue to work, continue to be me, and hopefully one of these days my name is called and I'll be a starter and that's that."
A couple weeks later, in late November, he expressed frustration to a reporter in Toronto.
After a loss to the Raptors, a reporter began to ask him about Dragic giving up minutes, playing only 21 that night. "It's always me," Thomas interrupted, looking and sounding frustrated. "It's always me."
"You gotta be ready when your name is called," he said later. "But I'm not going to sugarcoat it. It's tough. It's not what I expected. But coach has a tough job. Putting all of us on the floor and trying to mix up the minutes, it's tough for him. So it's not just tough for us as players, we just gotta be ready when our name's called and just know, I mean, coach is trying to do what he thinks is best for the team to put us in a position to win. But the key word is it's a tough situation. For all of us."
In mid-December, Thomas unloaded on David Aldridge of NBA.com when asked why he thought he'd get the playing time he wanted in Phoenix.
"I really went home, talked to my family, prayed on it. I really tried to envision how it would really work, 'cause it didn't make sense. But when they put it on paper and they told me I was going to be a big part of what they do here, I believed them. I felt like they were genuine. And we've had ups and downs this season, but at the end of the day we're trying to do the best we can to make it work. And if it doesn't work, it doesn't work. We tried. But we're doing the best we can to make it work and we're doing the best we can for this team."
After that, Thomas stopped dribbling to reporters as the Suns got into some winning ways by streaking to a 28-20 record on the back of a long home stretch.
It was only a losing stretch - 5 losses in 6 games - that put everyone back on edge. By that time, the Suns had had enough. Thomas complained too much too early, and then Dragic complained at the end.
Both were shipped out, and indirectly blasted for being too selfish out minutes over wins and losses. Suns fans knew the score, they knew the team didn't like playing together despite playing well once the ball rolled onto the court.
Thomas had a short memory though, just five days after the trade he wondered who the Suns were talking about.
"They told you that?" Thomas said when asked about his thoughts on the Suns front office saying certain players weren't content with their roles. "I mean, I do but who doesn't (want to start). It is like a bad thing if you tell someone you want to start, I don't get that. I was a team player and didn't complain to anybody and did my job. The guy who complained you seen it in media, I didn't say anything."
Ummm, sure, Isaiah.
Now Thomas is thriving in Boston, and he's getting that taste of the playoffs he's always wanted.
Maybe after he reflects on this season, he will realize it doesn't matter if you start or not. It's just a matter of how much impact you have on the team.