 
An election was held on November 6, 2018, to elect 25 members to Montana's Senate. The election coincided with elections for other offices, including the U.S Senate, U.S. House of Representatives, and state house. The primary election was held on June 2, 2018.
Results summary.
Close races.
Districts where the margin of victory was under 10%:
Detailed results.
Districts 1–22.
District 1.
Incumbent Republican Chas Vincent has represented the 1st district since 2011. Vincent was term-limited and couldn't seek re-election.
! scope="col" colspan="2" style="width: 15em" |Party
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District 4.
Incumbent Republican Mark Blasdel has represented the 4th district since 2014.
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District 5.
Incumbent Republican Bob Keenan has represented the 4th district since 2015.
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District 8.
Incumbent Democrat Lea Whitford has represented the 8th district since 2015. Whitford didn't seek re-election.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 9.
Incumbent Republican Llew Jones has represented the 9th district since 2011. Jones was term-limited and successfully ran for a seat in the state house.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 11.
Incumbent Republican Edward Buttrey has represented the 11th district and its predecessors since 2011. Buttrey was term-limited and successfully ran for a seat in the state house. State Representative Tom Jacobson, a Democrat, won the open seat.
! scope="col" colspan="2" style="width: 15em" |Party
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
District 12.
Incumbent Democrat Carlie Boland has represented the 12th district since 2017.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 13.
Incumbent Republican Brian Hoven has represented the 13th district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 14.
Incumbent Republican Russel Tempel has represented the 14th district since 2017.
! scope="col" colspan="2" style="width: 15em" |Party
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
District 19.
Incumbent Republican Eric Moore has represented the 19th district and its predecessors since 2011. Moore was term-limited and successfully ran for a seat in the state house.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
District 20.
Incumbent Republican Duane Ankney has represented the 20th district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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District 22.
Incumbent Republican Douglas Kary has represented the 22nd district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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Districts 24–50.
District 24.
Incumbent Democrat Mary McNally has represented the 24th district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
District 27.
Incumbent Republican Cary Smith has represented the 27th district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 29.
Incumbent Republican David Howard has represented the 29th district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 30.
Incumbent Republican Nels Swandal has represented the 30th district since 2015. Swandal didn't seek re-election.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 32.
Incumbent Republican Jedediah Hinkle has represented the 32nd district since 2014. He lost re-election to Democrat Pat Flowers.
! scope="col" colspan="2" style="width: 15em" |Party
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
District 33.
Incumbent Democrat Jennifer Pomnichowski has represented the 33rd district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 34.
Incumbent Republican Gordon Vance has represented the 34th district since 2015.
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! colspan="3" style="text-align:right;" | Total votes
District 41.
Incumbent Democrat Mary Caferro has represented the 41st district and its predecessors since 2011. Caferro was term-limited and successfully ran for a seat in the state house. State representative Janet Ellis won the open seat.
! scope="col" colspan="2" style="width: 15em" |Party
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
District 42.
Incumbent Democrat Jill Cohenour has represented the 43rd district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 43.
Incumbent Republican Pat Connell has represented the 43rd district since 2015. Connell lost re-nomination to fellow Republican Jason Ellsworth.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 48.
Incumbent Democrat Nate McConnell has represented the 48th district since 2018.
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! colspan="3" style="text-align:right;" | Total votes
District 49.
Incumbent Democrat Diane Sands has represented the 49th district since 2015.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Total votes
District 50.
Incumbent Democrat Tom Facey has represented the 50th district and its predecessors since 2011. Facey was term-limited and couldn't seek re-election. State Representative Bryce Bennett won the open seat.
! scope="col" colspan="2" style="width: 15em" |Party
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! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes