Mr McArthur received 7,238 votes, comfortably beating the SNP candidate Robert Leslie with 3,369, Conservative Sam Brown at 699 and Labour’s Colla Drake who received 290 votes.
However, the Lib Dem vote was down on 2016, with a 4.8 per cent swing to the SNP.
Turnout was 65.4 per cent – an increase on 62 per cent in 2016.
Mr McArthur has held the seat since 2007, when he took over from Liberal Democrat colleague Jim Wallace.
The second seat declared was Aberdeen Donside, which the SNP have held.
Jackie Dunbar was elected with 18,514 votes ahead of Harriet Cross on 9,488.
Turnout was 58 per cent, above 50.8 per cent in 2016.
Vote counting will take longer than usual this year amid Covid-19 restrictions and this year also saw a record number of postal votes cast.
The Electoral Management Board expects 48 of the 73 constituencies to be declared on Friday, including both the most marginal and most safe seats, as well as eight of the SNP's top ten target seats.
Airdrie and Shotts, and Coatbridge and Chryston are expected to follow Clydebank and Milngavie, with Cowdenbeath and Kirkcaldy also expected early on Friday afternoon.
Dumbarton, the most marginal seat formerly held by Jackie Baillie, is also expected to be declared on Friday.