Byrne resigned from her role as Black Cats chief executive in March following Adam Johnson’s conviction for child sex offences.
She was heavily criticised after Johnson claimed during his trial that he had made full and frank admissions to the club, and Byrne had all the messages exchanged between him and his victim and transcripts from police interviews.
She was central to the decision to allow Johnson to continue to play for Sunderland while on bail.
South Shields man jailed for terrifying physical and sexual assault on woman in her own home
Sea fret - a look at the foggy phenomenon which spoils sunny days in South Shields
Pair set up cannabis farm in town centre flat
Met Office announces yellow weather warning for thunderstorms across North East following heatwave
Campaigners rally against Local Plan after farmland in Cleadon earmarked for 156 homes
After less than four months out of the game, though, Byrne is back in football.
Her company, First For Players, is described as having a “player-centric philosophy” on its website.
It also presents the company as “specialists in top-flight sports management”.
Former Sunderland players have given their backing to Byrne as she launches her latest venture.
Ex-midfielder Graham Kavanagh tweeted: “Hope it goes well Mags. The game needs good agents like you X”
Striker Kenwyne Jones, meanwhile, added: “Have no doubt that you guys are gonna do well...... They’re the real deal ppl”
Former Sunderland assistant manager Fabrizio Piccareta, who was at the club while Paolo Di Canio was manager, posted: “All the very best Mags.”
The agency has been registered with Companies House, with an address in Penrith, having been set up in late-April. Byrne is listed as its sole director, and is also registered as an agent with the FA.
It marks a swift return to football for Byrne, who left the club in the aftermath of the Johnson case.
In a statement following her resignation, she said: “I recognise that, as CEO, my involvement with Mr Johnson and the decision to allow him to continue to represent Sunderland was a serious mistake.”
Sunderland had initially suspended Johnson for a fortnight following his arrest, but then allowed him back into the squad as the club fought relegation, and he was able to make a further 28 appearances.
He was then jailed for six years following a trial at Bradford Crown Court, after pleading guilty to grooming and one count of sexual activity with a child.
He was found guilty by a jury of one other charge, and was cleared of a further offence.
Byrne was involved with Sunderland for eight years, having been appointed club secretary in 2007 and chief executive four years later.
After she resigned, the club said in a statement: “Margaret, in her role as CEO, was responsible for the running of the club. She was also accountable for the actions taken by the club in relation to Mr. Johnson.
“Sunderland AFC acknowledges that Margaret’s intentions have always been to act in the best interests of the club, however it has become clear through our own internal investigations that in this instance decisions have been taken by Margaret in error.
“Whilst swift and decisive action was taken to terminate Mr. Johnson’s employment upon his guilty plea, decisions taken prior to this, including the decision not to suspend him for a second time pending the outcome of the trial, were wrong.”