Theivigan Panchalingham, 37, was previously a Serco guard at the Melbourne Immigration Transit Accommodation Centre in Broadmeadows.

Panchalingham, a refugee, is understood to have called the asylum seeker into his office at the detention centre between July and August, 2015. The woman complied and closed the door as she entered.

He offered her some food and tapped his thigh, in what she believed to be a gesture to sit on his lap.

She asked if she could leave the room. He helped her to open the door and kissed her on the cheek as she left.

Magistrate Meaghan Keogh earlier this month found the man guilty of one count of sexual assault for the kiss.

Ms Keogh said that while the assault was not the "most extreme", the woman was not free to leave detention or complain, making her "the most vulnerable type of victim".

"Because those people rely on you to ensure their safety it does make this offending behaviour a breach of trust of the most serious type," she said.

She also questioned Serco's failure to intervene after the guard sexually assaulted a fellow guard a year earlier, which she said could have prevented the more recent assault.

The asylum seeker told the court in a victim impact statement that she became afraid of most of the guards after the assault. She stayed in her room most of the time, sleeping only two to three hours each night.

"It has made me feel very unsafe and that rules and laws in Australia can't protect me. I feel I have no power, I have nothing to support myself, no one can make me feel safer," she said.

The woman, who has been living in the community since December, said she still had nightmares and was afraid of anyone who resembled Panchalingham.

Ms Keogh also said that Serco guards sent a clear message to detainees about what was acceptable in Australia through their actions, and he had undermined the woman's respect for the law.

She told Panchalingham that detainees were "fleeing all sorts of situations in their home countries and they're coming to another country where they hope they'll be allowed to live freely and with the protection of the law and that is something that you yourself have experienced," she said.

In the earlier 2014 incident, he kissed a colleague who was his junior on the mouth when they were en route to a Melbourne hospital for work, the Broadmeadows Magistrates Court heard.

His colleague yelled at him and later told her manager what happened but asked him not to make an official report, thinking that her yelling at the guard would prevent future attacks.

Ms Keogh said that Serco may have lost an opportunity to deal with the man's behaviour early on.

He pleaded guilty to one count of indecent assault in relation to this incident, for which Ms Keogh sentenced him to an 18-month community corrections order.

The order, which is to be served after his prison term, includes 200 hours' community service and participation in a sex offender program.

Defence counsel Shaun Pascoe told the court that the Tamil man was previously a journalist for a number of Tamil newspapers in Sri Lanka during the country's civil war, where he witnessed a bombing and other violence.

He said he came to Australia to study business administration at La Trobe University and later obtained a humanitarian visa to stay in Australia because he feared that his anti-government stance would put his safety at risk if he returned to Sri Lanka.

Mr Pascoe said his client had already lost his job at Serco and significant standing in the local Tamil community as a result of the allegations.

He unsuccessfully argued that he should receive a community corrections order without conviction for both his crimes.