The Police Investigations and Review Commission (PIRC) scheme will allow graduates and people with no investigative background to join it.
It will replace the existing Police Complaints Commission Scotland with the introduction of the single police force in April.
The new body will investigate criminal and serious misconduct allegations against the police, as well as deaths with police involvement.
Currently, other police forces perform this function, but this will no longer be possible when the eight forces are merged as Police Scotland from April 1, 2013, led by chief constable Stephen House.
Successful applicants will train for two years, through a specialist course and on-the-job experience, before becoming fully qualified members of the PIRC's investigations team.
Former CID boss John Mitchell, director of Investigations for the watchdog, claims the trainees who complete the scheme will go on to be the "lifeblood" of the organisation.
Mr Mitchell said: "I would like to initiate the scheme as soon as I can. We'll be advertising for applicants to the scheme in the not too distant future."
The trainees will be given specialist teaching on an accredited course. However, a decision has yet to be made on which university or college that will take place.
The programme will then provide on-the-job training with the support of other members of the PIRC investigations team.
Mr Mitchell, who retired as head of CID for Strathclyde Police in July, said: "It's still early days but we're working closely with other oversight bodies in the UK and Northern Ireland and taking the learning that they've had over a number of years.
"There are a number of courses already out there but we have to find someone or some place here that can deliver the training from a Scottish perspective.
"We have to look at what other organisations are doing and take the best of it and make it fit out needs."
The trainees will form part of a team of 23 investigators, including Mr Mitchell.
This is likely to include a head of investigations, three senior investigators, six deputy senior investigators and 12 further investigators, some of whom will be trainees.
Mr Mitchell added: "We need to get the right balance of people who can do the job effectively and do it from day one on April 1."
The commission will carry out investigations into criminal allegations and deaths on behalf of the Crown Office, who will then decide whether or not to prosecute or hold a Fatal Accident Inquiry.
The body will also carry out investigations into misconduct.