The 24-time major champion defeated Lorenzo Musetti 6-4 6-2 to ensure he would walk away from Roland-Garros with a medal.
Djokovic will now face number two seed Carlos Alcaraz in a rematch of last month's Wimbledon final.
The 37-year-old was aware of the enormity of the achievement in going one step further, having suffered semi-final losses to Rafael Nadal, Andy Murray and Alexander Zverev in three previous Olympic semi-finals, though he did claim bronze at the Beijing Games in 2008.
"I have been waiting for this for almost 20 years," Djokovic said in his on-court interview.
"I've played four Olympic Games, this is my fifth and '’ve never passed the semi-finals. I lost three semi-finals in my first four Olympic Games.
"I managed to overcome this big hurdle. I must be honest and say that I was thinking about all the semi-finals that I lost."
The Serbian had to overcome injury concerns after his quarter-final match against Stefanos Tsitsipas, and Djokovic was more encouraged by his mental strength against an opponent that has made great strides on the ATP Tour this season in Musetti.
"I just tried to be in the present moment. I played against a player who is in great form and really came out firing from both ends," Djokovic added.
"I just tried to maintain the focus and do what I have to do."
Sunday's final between Djokovic and Alcaraz will be the seventh meeting between the pair, with the head-to-head currently at three apiece.
The 20-time grand slam champion was knocked out of the French Open at the semi-final stage by eventual winner Novak Djokovic.
And, with just a two-week gap to the grass-court slam in London, the 35-year-old has opted against taking part at the All England Club or the Games in Tokyo.
"Hi all, I have decided not to participate at this year's Championships at Wimbledon and the Olympic Games in Tokyo," the Spaniard tweeted.
"It's never an easy decision to take but after listening to my body and discuss it with my team I understand that it is the right decision.
"The goal is to prolong my career and continue to do what makes me happy, that is to compete at the highest level and keep fighting for those professional and personal goals at he maximum level of competition."
Nadal explained that the quick turnaround from a gruelling campaign in Paris to another tough schedule at Wimbledon presented too much of a risk to his fitness.
"The fact that there has only been two weeks between RG [Roland Garros] and Wimbledon didn't make it easier on my body to recuperate after the always demanding clay court season," he said.
"They have been two months of great effort and the decision I take is focused looking at the mid and long term.
"Sport prevention of any kind of excess in my body is a very important factor at this stage of my career in order to try to keep fighting for the highest level of competition and titles.
"I want to send a special message to my fans around the world, to those in the United Kingdom and Japan in particular.
"The Olympic Games always meant a lot and they were always a priority as a Sports person, I found the spirit that every sports person in the world wants to live. I personally had the chance to live 3 of them and had the honor to be the flag bearer for my country."
Nadal is a two-time Wimbledon champion and took gold at the 2008 Olympics in Beijing.
