It was expected that the Greece striker would be on his way after six and a half years in the east end of Glasgow but it was also believed that the champions would make him an offer to stay.
Manager Neil Lennon watched Samaras score from the spot after coming on as a second-half substitute, either side of goals from Anthony Stokes and Kris Commons, with Filip Twardzik scoring an own goal for United, and said: "I would imagine his mind is made up" - suggesting that the former Manchester City forward had a decision to make.
However, Samaras told BBC Scotland: "I'm leaving, that's for sure, but it was not my decision.
"I never had an offer from the club. I never had an offer from Peter Lawwell. I have been seven years at the club and I would have loved to stay.
"I had a chat with the manager. He would have loved me to stay and I was happy to stay, but me and the gaffer don't make the decisions - there are people higher up.
"I have not spoken to any other club. I was waiting to the end to see if they offered me anything, but that is the end."
Lennon watched with pride as skipper Scott Brown was presented with the trophy after the last game of the season which allowed the Northern Irishman to join Willie Maley, Jock Stein and Gordon Strachan in an elite group of Celtic managers who have won three consecutive titles with the Parkhead club.
He said: "It's very special to win any sort of trophy.
"For a long time in the '80s and '90s it was a struggle for us but now we are very productive in terms of picking up trophies and being successful on and off the field.
"I'm very proud to have joined that select band of Celtic managers. I'm one of the few who have been privileged enough to do this job and when you are here you want to make the most of it.
"We can be pretty proud of what we have achieved in the last four years."
Celtic defender Charlie Mulgrew claimed winning titles was not easy when "everybody is waiting for you to fail".
He said: "It's always good to win the title and lift the trophy, it's harder than a lot of people think at times.
"You are under a lot of pressure and there are a lot of expectations. So we are delighted to have done it in the manner which we did. It's not easy winning titles so this was great. It's never as easy as it's made out and the expectations are always there.
"To go through the campaign with just one defeat is very pleasing."
While Samaras is on his way to pastures new, Virgil van Dijk was somewhat coy when asked if he would still be at Celtic Park next season.
The Dutch defender told Sky Sports: "I still have a contract until 2017 but in football you never know what can happen so we will see.
"I've really enjoyed our league campaign which has been great. But in the cups it has been a little bit disappointing this season. I think next season we will do a lot better."
With one eye on the William Hill Scottish Cup final against St Johnstone at the same venue on Saturday, United boss Jackie McNamara left top players Nadir Ciftci, Stuart Armstrong, Andrew Robertson and Gary Mackay-Steven on the bench.
The former Celtic defender said: "The focus is on next week but I thought it was a professional performance.
"I am not too disappointed. I thought we passed it well and were well organised.
"We left a few of the more forward players on the bench, you have seen the craft of Mackay-Steven and Armstrong when they came on."