Laszlo was earlier given the boot after 18 months in charge when majority shareholder Vladimir Romanov finally lost patience with his repeated complaints about Hearts' transfer policy.
The controversial Romanov could hardly have acted more swiftly, prompting suspicions this move had been in the pipeline for a number of days.
Jefferies stood down as Kilmarnock boss on January 11 after almost eight years in charge at Rugby Park.
He made no secret of his desire to return to the game as quickly as possible and had been linked with the vacancies at Dundee United and Motherwell before both clubs appointed Peter Houston and Craig Brown, respectively, until the end of the season.
Jefferies was the last manager to lead Hearts to a major trophy, masterminding their 1998 Scottish Cup triumph over Rangers.
He also led them to four top-four finishes in the Scottish Premier League in five years before moving to the English Premier League with Bradford.
Jefferies, who also captained the Jambos during his playing career, told the club's official website: "It did not take me too long to have a chat with them as everyone knows I have supported, played and managed the club.
"Everyone knows the affection I have got for the club.
"I think over the years a lot of people have linked me with the job a couple of times and there was a groundswell of hope.
"I didn't give it any thought until I got the call this afternoon. It is unbelievable to have been spoken to in connection with the job.
"It is like any job that you feel for a manager when he goes out. If I did not get it, someone else would.
"The discussions went well and I know how things work in the club and now we've got to a stage where it is just a fantastic feeling to be back involved at the club again.
"Hopefully people will be happy with that."
Despite Hearts being around £30million in debt, Jefferies believes he is taking over at "a great time".
"We're in the top half and we're in a cup semi-final. It is very positive," he said.
"It is not often a manager can come back and it has been nine years.
"Hopefully we can use the experience gained in that time.
"Although I am a bit older, the passion is still there for this club."
Hearts director Sergejus Fedotovas added: "We recognise Jim Jefferies is a man that understands Heart of Midlothian Football Club and our supporters.
"We believe that he has the ability to realise the full potential of a very good squad of players.
"He was the board's unanimous choice to become manager and we wish him every success in returning to Tynecastle."
St. Johnstone v Hearts Win to Nil: Hearts 7/2
Source: Team Talk
Source: Team Talk