Being arrested for driving under the influence (DUI) in Ontario is a stressful and overwhelming experience. Whether the stop happens during a routine traffic check, after a collision, or because an officer suspects impairment, the process can feel intimidating — especially if you don’t know your rights or what police are legally permitted to do.
A DUI charge can have life-changing consequences: licence suspension, fines, criminal records, increased insurance premiums, travel restrictions, and even jail in severe cases. Because the stakes are high, it’s essential to understand how the DUI arrest process works, what police must follow, and where legal defences often arise.
This article provides a clear, evergreen, Ontario-specific breakdown of the entire DUI arrest process — from the initial traffic stop to post-arrest procedures — and explains how experienced DUI defence lawyers challenge unlawful police actions, improper methods, and Charter rights violations.
Since the Criminal Code amendments in 2018, police in Ontario have the authority to stop any driver to conduct a sobriety check — even without observing erratic driving or signs of impairment. This is known as mandatory alcohol screening.
While mandatory screening increases enforcement, it does not eliminate the requirement that police follow constitutional protections. Any DUI arrest must still comply with:
If officers fail to comply with these rules, the defence may be able to suppress evidence or challenge the validity of the arrest .
While random stops are allowed, most DUI arrests begin for predictable reasons:
In most cases, the officer begins by asking for your licence, insurance, and registration while observing your speech, coordination, and smell of alcohol or cannabis, as well as your behaviour.
You do not have to answer “Have you been drinking?”
Anything you say can be used as evidence.
After the initial interaction, the officer may legally demand one of the following:
Police do not need suspicion of impairment to demand this test.
Refusing is a criminal offence with the same penalties as a DUI conviction.
A result of:
Used when a breath device is unavailable or when drug impairment is suspected.
This includes assessing:
Failing the SFST typically leads to arrest.
Used less frequently, but legal. Detects THC, cocaine, and methamphetamine
Once an officer forms reasonable grounds to believe you are impaired or over 80, they must:
You may be handcuffed and placed in a cruiser.
Your vehicle may be searched or towed.
You still have the right to remain silent — and should use it.
As Brian Brody, Criminal Defence Lawyer Partner at Mass Tsang , notes:
“After the arrest, the biggest mistake people make is talking too much. Anything you say becomes evidence. Invoke your right to silence until you speak with a lawyer.”
At the station, you will undergo formal testing that determines which offence you will be charged with. Police may require:
For suspected drug impairment, a certified Drug Recognition Expert (DRE) conducts a multi-step assessment examining:
Blood samples are used in:
You must be given:
If police fail any of these obligations, the defence may ask the court to exclude the results.
Strict timing and procedural requirements protect drivers from unreliable or unconstitutional testing. Police must ensure:
Failure to comply allows defence lawyers to argue for the exclusion of breath or drug test results.
As Robbie Tsang, Criminal Defence Lawyer & Managing Partner , explains:
“In many DUI cases, the legal defence doesn’t focus on the alcohol level but on whether police followed the law. One procedural error can be enough to win a case.”
After processing, you may be released on:
Police typically release individuals when they have a safe way home and no aggravating factors.
You may be held for a
bail hearing
if:
Based on results and observations, charges may include:
These charges carry:
Experienced defence lawyers analyze every moment of the arrest to identify procedural errors or Charter violations. Common defence avenues include:
A single breach may be enough to exclude all test results and dismiss the case.
| Testing Stage | What Happens | Legal Requirements | Defence Issues |
|---|---|---|---|
| Roadside | Screening device or SFST | Must occur promptly; no suspicion needed | Delayed test, unreliable device, improper demand |
| Transport to Station | You are detained and taken to the station | Must be reasonable and efficient | Unreasonable delay affecting test results |
| Breathalyzer/DRE | Formal evidentiary testing | Qualified technician; strict timing | Device issues, Charter rights violations |
| Post-Testing | Charges determined | Crown relies on results | Defence examines each procedural step |
During a DUI arrest in Canada, you have the following legal rights under the Charter of Rights and Freedoms:
Why this matters: If any of these rights are violated, your lawyer may argue to exclude the resulting evidence, which can lead to reduced or withdrawn charges.
If you’ve been arrested for DUI in Canada, taking the proper steps immediately can protect your rights and improve your legal defence. Here’s what to do:
Why it matters: These actions preserve key evidence and can help your defence lawyer challenge the legality of the stop, arrest, or testing procedures.
With more than 30 years of experience in DUI defence across the GTA, the lawyers at Mass Tsang LLP focus on:
This meticulous approach has resulted in hundreds of dismissed, reduced, or withdrawn DUI charges.
A DUI charge is serious, but a conviction is not inevitable. Many cases are won because police made errors, ignored Charter protections, or failed to follow strict technical requirements.
If you’re facing a DUI charge in the Greater Toronto Area, Mass Tsang LLP can help.
Contact us today for a free, confidential consultation.
The sooner you get legal advice, the stronger your defence will be.
Yes. Mandatory alcohol screening laws allow police to stop any driver at any time without suspicion of impairment.
Refusing a breath test is a criminal offence and carries penalties equal to or greater than a DUI conviction.
Police must conduct evidentiary breath testing within three hours of the time you were driving. Unreasonable delays can result in evidence being excluded.
No. You have the right to remain silent, and anything you say can be used against you.
Yes. Cases are often dismissed when police fail to follow proper procedures or violate Charter rights.
Yes. DUI law is complex, and having an experienced lawyer significantly improves your chances of a favourable outcome.
