The ITV show, which sees Clunes as a grumpy, blood-phobic medic working in an idyllic Cornish village, aired its last episode on Wednesday night with one final Christmas special planned for December.
It was an emotional final instalment as the doctor had been offered a prestigious new job at Imperial College in London and was preparing to move with wife Louisa (Caroline Catz) and their two young children, leaving their beloved community behind.
However, a last-minute chase after a missing dog lead to Martin having a grisly accident involving tearing an artery in his arm – his worst nightmare because of his blood phobia.
Viewers were worried that he would be killed off in the show's finale, but Martin pulled through and decided to stay in Portwenn rather than leaving for London.
The episode had viewers in tears, as one fan tweeted: "Can't believe that's it now. The last ever Doc Martin. What a series."
Someone else wrote: "Oh what a brilliant ending!!! Crying my eyes out. Just fab. Thanks for everything Doc!"
Another viewer commented: "What a roller coaster of emotions that final episode gave me. Surely I wasn’t the only one who genuinely thought we were about to lose Doc?! Heartwarming episode!"
Fans also shared their sadness at the series being over.
One person tweeeted: "Have thoroughly enjoyed the characters and stories. Brilliant cast and great writing in my humble opinion. It’s been a comforting staple. Thank you to all those in front and behind the camera these last few years, for the utterly brilliant #DocMartin"
Someone else wrote: "Doc Martin has been in my life for 18 years! And to see it is now over is quite upsetting. It always brought me such joy to watch and we'll never see another show like it again. I will miss it so much."
But another fan added: "thank goodness the Doc is staying in Port Wenn. What a fabulous episode and what a lovely ending. Roll on the Christmas special."
Watch: Doc Martin cast and crew complete last ever scenes in Port Isaac