Initially, casual employees were only engaged in work on an as-needed basis, worked irregular shifts and their employment period would start and end on the hours they worked. Due to such irregularity, it was impractical for dismissal rights to be extended to them.
However, with the evolution of company structures, casual employment has evolved and it has become more common for companies to depend on the regular availability of their casual employees to sustain business. To keep up with this modern workplace structure, the Fair Work Act 2009 (Cth) extended the eligibility of unfair dismissal claims to casual employees who fulfil the following criteria:
HAVE I BEEN UNFAIRLY DISMISSED?
To be unfairly dismissed, your employment must have been dismissed at your employer’s initiative (section 394) and the dismissal must have been harsh, unjust or unreasonable. There is no express definition of what may be harsh, unjust or unreasonable, however, Section 387 provides considerations that the FWC must take into account when making a decision. This includes:
Too read more about what details should be included into a claim for unfair dismissal, see, https://employmentlawonline.com.au/what-should-i-include-in-my-unfair-dismissal-application/
HAVE I BEEN EMPLOYED THROUGH THE MINIMUM EMPLOYMENT PERIOD?
You must have been employed for the minimum employment period applicable to your employment. This depends on whether your employer is a small business employer section 382 > definition directs to (section 383);
DID I HAVE REASONABLE EXPECTATION OF ONGOING EMPLOYMENT?
There is no express definition of “reasonable expectation of ongoing employment” and this will vary on a case by case basis.
In the case of Ponce v DJT Staff Management Services Pty Ltd T/A Daly’s Traffic, Roe C applied a test of “whether or not during a period of at least six months.. the employee had… reasonable expectation of continuing employment on a regular and systematic basis.”
Some indicators that may point to reasonable expectation of ongoing employment include:
You may not have reasonable expectation of ongoing employment if:
DID I WORK ON A REGULAR AND SYSTEMATIC BASIS?
In assessing whether you work on a regular and systematic basis, you will only need to consider the employment, and not the hours that you work.
  FWA 2078
 Yaraka Holdings Pty Limited v Giljevic  ACTCA 6 (30 March 2006)
 Above n1.
If you are a casual employee and fulfil all the above-mentioned criteria, you will be eligible to make an unfair dismissal claim against your previous employer.