"We've run out of runway," he told CBC News.
As of Monday, there are just 17 sitting days left on the calendar before the Commons shuts down for the summer — which, given the looming fall election, is likely the end of the line, as far as unfinished legislation.
Bill C-53, which was introduced in March, would eliminate parole for those convicted of first-degree murder involving sexual assault, kidnapping, terrorism or the killing of a public officer, or in a particularly brutal killing.
And although he acknowledged at the time that it would apply to "a relatively small number of offenders," MacKay stressed it would ensure those convicted of especially heinous crimes would "take their last breath behind bars."
Budget bill currently the top priority: MacKay
Since then, however, the bill has languished at first reading.
Given the dwindling timeline, the current priority is shepherding the spring omnibus budget bill, C-59, through both the House and Senate before time runs out, MacKay said.
MacKay's hopeful, though, that his efforts to better protect police dogs and other service animals will make it to royal assent before the curtains close on the 41st Parliament.
The House justice committee reported that bill back without amendment on May 8, although without all-party support, it would likely take several days before it could be sent to the Senate.
Last week, MacKay announced he would be stepping down at the next election, although he is expected to stay on as justice minister until then.