However, just two miles into the marathon, she was stopped by the race director, Jock Semple, who demanded that she hand over her bib and leave the race.
On Monday, her bib number, 261 - the same one she wore in 1967 - became only the second number ever to be retired in Boston Marathon's history.
Fifty years on, aged 70, Ms Switzer returned to the starting line wearing the same number.
Anoher woman, Bobbi Gibb, had unofficially completed the 26.2-mile course a year earlier, popping out of the bushes after she was denied an official bib.
In the women's race, Kiplagat conjured a similarly decisive burst over the closing stages to claim the race for the first time. She was also given the honour of firing the gun for the women's elite runners, which flagged off the marathon.
"It's beyond me; it's the number now", said Switzer, who ran the race on Monday along with 118 women and "seven intrepid men" who raised money for the charity that uses running to improve women's lives around the world.More news: Tip-in by Ryan lifts Senators over Bruins 4-3 in overtime
"I felt really blessed to have her out there running every step with me and that gives me a lot of strength in the marathon and is what helped me get through the distance", she says.
The finish capped off a big weekend for Switzer, who ran with 125 charity runners for her 261 Fearless foundation.
Switzer completed this year's race only a little slower, in 4:44:31. The Boston Marathon officially admitted women in 1972 and Ms. Switzer's ardent effort at advocating running for women saw the event being included in the Los Angeles Summer Olympics of 1984. Now 58% of marathon runners in the USA are women.
Running the 1967 Boston Marathon changed the course of Switzer's life.
"It was a very good thing she wasn't well-behaved on that morning", said Joann Flaminio, the first female president in the 125-year history of the B.A.A.
Over the years, Switzer has competed in more than 30 marathons, winning NY in 1974 in 3:07:29, and has worked as a television commentator.