Ryan James Parnell, 36, faced sentencing on Thursday after pleading guilty to one count of using a carriage service to procure an underage person to engage in sex, believing them to be underage.

He accepted an Instagram follow request from a fictitious account purporting to be a 15-year-old girl in January 2022.

It was his then-girlfriend who lived with him at the time.

Months earlier, she confronted him after another woman told her she had been asked for nude photographs from an account called "billybobdude4343".

Parnell told her: "I'm going to delete it. I'm not using it anyway."

After accepting the request, Parnell messaged the account to ask if she had an OnlyFans account.

"She replied she was 15 and therefore did not have an OnlyFans account," Judge Andrew Scotting said on Thursday.

Parnell continued messaging the account, using two separate accounts, sending videos of himself masturbating that he wanted reciprocated, and describing sex acts he liked to engage in with young girls.

Some of the messages from the fictitious account encouraged or solicited sexualised responses, Judge Andrew Scotting said in Sydney's Downing Centre District Court on Thursday.

"(Parnell's partner) probably committed the same offence but she has not been charged," the judge said.

She reported him to police.

Her behaviour was different to police targeting people in chatrooms and online spaces known to attract pedophiles, occurring in the direct messages of a widely used social media platform, and with no evidence Parnell had any such proclivities, the judge said.

However, Parnell was previously convicted of offences including a registrable child sex offence, occurring when he was aged between 13 and 19 involving a child about three years younger than him.

Judge Scotting said he has rebuilt his life in a productive way since but that offending had activated a mandatory minimum non-parole period of four years.

The appropriate sentence for his latest "unique case" was well below that minimum.

Parliament had ruled a sentence must be imposed and the judge sentenced Parnell to two years and 10 months imprisonment to expire in March 2026, a sentence he immediately suspended, finding exceptional circumstances.

"His partner has sought to use the criminal law for her own purposes," the judge said.

"She knew of his criminal history and sought to use it against him as a means of controlling him."

Parnell has been immediately released, required to post $1000 recognisance and be of good behaviour for five years.

1800 RESPECT (1800 737 732)

National Sexual Abuse and Redress Support Service 1800 211 028

Australian Associated Press