Jennings has become a mainstay at the top of Lancashire’s County Championship side since joining from Durham ahead of the 2018 season, as well as excelling in 45 limited-overs appearances during that time.
A former captain of England Lions, the left-hander has scored 7,932 First-Class runs since making his debut in 2011, scoring 19 centuries and 31 half-centuries.
Jennings marked his Test debut with a century against India at Wankhede Stadium in 2016 and added a second three-figure score in making 146 vs Sri Lanka at Galle during the 2018 tour.
For the Red Rose, he has notched approaching 2,000 First-Class runs in 38 appearances, scoring four centuries with a best of 177 at Worcestershire.
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In the 2021 campaign so far, Jennings averages 43.10 after hitting one century against Yorkshire at Emirates Old Trafford last month, in addition to three half centuries.
He has been a revelation in One-Day Cricket, scoring nearly 800 runs at an average of over 52. His total of 375 runs in 2018 was a team-high, followed by 416 runs one year later as Lancashire reached the semi-finals.
In 2019, Jennings did not miss a single game across all three competitions as he helped the CLub to an unbeaten promotion season from Division Two and progress into the knockout rounds of Vitality Blast.
In the opening game of Vitality Blast 2020, Jennings smashed his maiden T20 century against Durham at Emirates Riverside, scoring 108 off 63 balls against his former Club.
The 29 year-old, who is currently studying for a Masters, has also contributed in the commercial department at Emirates Old Trafford throughout the off-season.
Jennings said: “I’m delighted to commit my future to Lancashire. I have immensely enjoyed my time here so far and it was a no-brainer when it came to discussing a contract extension.
“At 29 I have experienced so much in the game already at domestic and international level that I can pass on to the next generation of players, but I’m also coming into a prime age for batsmen and hope I can put together some big, match-winning scores.
“It’s an honour to be part of a Club with such big tradition, but also one with a squad filled with such talent. It’s an exciting time for Lancashire and as a group, we're all desperate to compete for silverware over the next couple of years."