The former Celtic full-back, who completed his deal earlier this week, had already trained with Ian Baraclough’s side prior to their play-off first-leg against Rangers at Ibrox, a match which the visitors won 3-1.
However, he admits the move remained in the balance until the second leg, which Motherwell won 3-0 to complete a 6-1 aggregate victory which consigned Stuart McCall’s side to at least another season in the Championship.
Speaking to Sky Sports News HQ, 21-year-old Chalmers, who has represented Scotland at every level from U16 to U21, said: “I came in and trained on the Monday and Tuesday.
“I then had a chat with the manager and he said they quite liked what they had seen but I still wasn’t sure what was going to happen.
“However, I knew there was a slight possibility (the deal may not go through) so I watched both legs and was definitely supporting Motherwell to get the job done.”
Meanwhile, Motherwell general manager Alan Burrows says fans can expect ‘a very different Motherwell next season’ after the manager overhauls his squad.
Sixteen players have left this week and around 10 could come in as Baraclough aims to avoid a repeat of the relegation battle his side endured last season.
“OK there is a still a good core of experienced lads like Keith Lasley, Stevie Hammell and Stephen McManus, the mainstays of the squad who have been here for a number of years and who will still be here, which is great.
“But there will be a radically different Motherwell team, or squad at least, come the new Premiership season.”