"Inappropriate touching hurts, and it stays with you for a long time," Capstick told host Evan Solomon.
He says he was sexually harassed on a regular basis by one MP and in another circumstance, says he was sexually touched by another MP. He says he told the second individual at the time that it was inappropriate.
Capstick says he didn't report either man's behaviour.
"Why did I do that at the time? Because I felt powerless," Capstick said.
"You feel absolutely without power to be able to report somebody who is 30 or 40 years, in some instances, your senior and is perhaps at a status where you just simply as a 21-year-old can't challenge that person."
Capstick worked on the Hill between 2002 and 2008, first for the Liberal party and then as a press secretary for the NDP. He's now managing partner at MediaStyle, an Ottawa-based communications strategy company.
'Jian Ghomeshi affair has allowed people to come forward'
Capstick's comments came during a Power & Politics panel conversation about two Liberal MPs who were suspended from caucus on Monday because of harassment allegations.
Capstick says the suspensions as well as the allegations against former CBC host Jian Ghomeshi for sexually aggressive and abusive behaviour compelled him to publicly share his experience.
"The Jian Ghomeshi affair has allowed people to come forward, creating a very different style of conversation," Capstick said.
Capstick wasn't planning to talk about his experience on live television, but once the panel discussion started, he says he decided to open up about his personal story.
Identities of two former MPs
Solomon asked Capstick if he'll name the two former MPs he says sexually harassed him.
Capstick responded that he's going to have a conversation with his family to figure out how to proceed.
He added that sexual harassment on Parliament Hill is too common an occurrence.
"People have been harassed both physically and sexually on Parliament Hill for a very long time," he said.