The second-half substitute struck with time running out after the Jags had dominated for most of the match but trailed to Stevie May's early opener.
Doolan's goal was his first in the last 15 matches and denied St Johnstone a third successive victory but was no more than they merited for a lively display that only lacked a better cutting edge.
May's eighth-minute breakthrough was his 23rd of the campaign and came after he had been rested in midweek for the win over St Mirren.
St Johnstone welcomed back manager Tommy Wright for the game after the Northern Irishman had been forced to miss his team's last two matches through ill-health.
The Perth boss was taken to hospital almost a fortnight ago with stomach pains and underwent an operation on his gallbladder that resulted in him staying away from the victory over Hibs last weekend, in which Saints secured a top-six finish, and the midweek triumph over St Mirren.
Wright had remained in charge of team selection but was deemed fit enough to play a more active role for this 90 minutes as he took his place in the directors' box.
Partick were neat and tidy in initial sparring after kick-off but St Johnstone proved the side most likely to threaten either goal in the opening exchanges.
Jordan McMillan's last-ditch tackle prevented Saints' Michael O'Halloran from pulling the trigger 12 yards from goal in the sixth minute and just moments later home full-back Dave Mackay did get his shot away from a Lee Croft corner but his effort sailed wildly over.
However, the Perth men's eighth-minute breakthrough was fortuitous, even if the identity of the scorer was no surprise.
A midfield ricochet fed the ever-dangerous May and his eventual shot beat Paul Gallacher to the keeper's right with the aid of a lucky deflection off Thistle defender Lee Mair.
Partick's response with impressive and four minutes later St Johnstone keeper Alan Mannus was brought into action to make a save low to his left from a Prince Buaben shot.
After just another 60 seconds, Thistle came close again. Lyle Taylor held up possession on the right and Gary Fraser's sweeping cross from the striker's lay-off was headed just inches over by Chris Erskine.
Erskine was at the heart of almost all of the visitors' attacks and the on-loan Dundee United midfielder threatened with a driving run at the Saints defence, only to see his shot drift across the target and wide.
Yet, for all Partick's control of the ball and patient play, it was the home side who came within a whisker of a second in the 20th minute.
Croft was allowed to run too far before stinging the palms of Gallacher with a powerful drive but the predatory May was unlucky to see his follow-up header come back off the crossbar and cleared to safety by the Thistle defence.
The Jags were by far the more comfortable in possession as the half wore on and would have been mystified as to how they went in for the interval a goal down.
They began the second period the way they had ended the first, dictating the flow and tempo of the game.
But, again, it was St Johnstone who carved out the first real opportunity with a more direct approach. A long ball was allowed to drift over the Thistle defence with May chasing but Gallacher was equal to Steven MacLean's eventual effort from 16 yards out.
Partick continued to push at the other end and on the hour mark Erskine could not quite get enough curl on his shot that was whipped towards the top corner from the left side of the area.
Two minutes later, Saints defender Frazer Wright was brave as he threw his body in the way of Gary Fraser's powerfully-hit drive that looked set to trouble the worried Mannus behind.
However, Mannus was finally beaten with just seconds left in the 90 minutes when Doolan picked up a loose ball on the edge of the area and found the net with a low drive that was too strong for Mannus to handle.