Prof John McNeill will now be able to carry out probes into serious incidents involving the police, rather than senior officers from other forces.
His annual report showed he dealt with 27% more cases in the year to March 2013 than in the previous year.
He said the rise showed the “confidence the public has in this office”.
The report also showed a 5% rise in requests from the public for scrutiny over how police managed their complaint against officers to 542, of which 174 were accepted for review.
Members of the public can ask the commissioner to review the way the police have handled their complaint.
In cases where the commissioner finds a failing in the police handling of a complaint he can make recommendations, including an apology to the member of the public or order further investigations by police.
During the year, he published 143 reports, with almost 60% of the cases found to have been handled to a reasonable standard by the police.
Prof McNeill said: “The prospect of a single police service in Scotland threw up a number of challenges for me during the year around ensuring that I would have a team that was operationally ready to carry out independent and effective investigations from April 1.
“I am pleased to be able to report that this was achieved, as the addition of an independent investigative function to my remit marks a significant change for Scotland and raises the bar in how we hold the police to account.”
His office will be re-named the Police Investigations & Review Commissioner (PIRC) to reflect its expanded remit.
The creation of the new single Police Scotland service means it is no longer possible for senior officers from other forces to investigate serious complaints.