Grosicki scored early in each half to earn the three points and keep the Tigers in the race for a play-off place.
Jordy de Wijs and Daniel Batty return to Hull City’s starting eleven for this afternoon’s away game against Ipswich Town as two of four changes to Nigel Adkins’ line-up.
Eric Lichaj and Todd Kane also come in, with Liam Ridgewell, Kevin Stewart, Robbie McKenzie and Stephen Kingsley making way.
On a bright and warm afternoon in Suffolk, it was the visitors who went close to taking an early lead when Grosicki’s free kick was headed just wide of his own goal by an Ipswich defender.
The Tigers did open the scoring in the 14th minute. A ball in from the right found Fraizer Campbell inside the box and he unselfishly knocked it to his left for Grosicki to fire in with his left foot.
Grosicki looked to repay Campbell with a ball through to the striker a couple of minutes later but a defender got across well to shut down the space inside the area.
Myles Kenlock blasted a first Ipswich shot of the afternoon high over the bar after cutting in from the left before Gwion Edwards was booked for a late challenge on Lichaj.
Campbell limped off to be replaced by Chris Martin eight minutes before the break, with Ipswich going close to a leveller in the 43rd minute through Kayden Jackson but Lichaj was perfectly positioned to clear off the line.
The home side went close again in added time, and this time it was Marc Pugh clearing off the line from an Edwards header.
The Tigers made the most of those let-offs to double their lead five minutes after the break. The hard work was done by Jarrod Bowen who picked up possession midway inside his own half and went on a run that took him to the edge of the Ipswich box, before finding Grosicki who did the rest with a low right-footed shot that went in off the far post.
Alan Judge curled narrowly wide as the home side responded, while David Marshall was harshly booked just after the hour for allegedly time-wasting.
McKenzie came on for Burke with 16 minutes left and all that remained was for Grosicki to complete his hat-trick. He came close, seeing one effort ruled out for a foul in the build-up and another blocked, before being replaced by Evandro in the 87th minute. Marc Pugh hit an upright in added time at the end of a quick counter-attack, but two goals were enough for the win.
Ipswich Town: Bartosz Bialkowski, James Bree, Luke Chambers, Toto Nsiala, Myles Kenlock, Trevoh Chalobah, Cole Skuse (Idris El Mizouni 74), Jon Nolan (Andre Dozzell 18), Gwion Edwards, Alan Judge, Kayden Jackson (Collin Quaner 61).
Subs Not Used: Dean Gerken, Jonas Knudsen, Flynn Downes, Josh Emmanuel.
Hull City: David Marshall, Todd Kane, Reece Burke (Robbie McKenzie 74), Jordy de Wijs, Eric Lichaj, Daniel Batty, Jackson Irvine, Jarrod Bowen, Marc Pugh, Kamil Grosicki (Evandro 87), Fraizer Campbell (Chris Martin 37).
Subs Not Used: George Long, Kevin Stewart, David Milinkovic, Liam Ridgewell.
Referee: Mr J. Brooks.
Attendance: 15,720 (485 Visiting Supporters).